doc_content
stringlengths 1
386k
| doc_id
stringlengths 5
188
|
|---|---|
numpy.random.RandomState.triangular method random.RandomState.triangular(left, mode, right, size=None)
Draw samples from the triangular distribution over the interval [left, right]. The triangular distribution is a continuous probability distribution with lower limit left, peak at mode, and upper limit right. Unlike the other distributions, these parameters directly define the shape of the pdf. Note New code should use the triangular method of a default_rng() instance instead; please see the Quick Start. Parameters
leftfloat or array_like of floats
Lower limit.
modefloat or array_like of floats
The value where the peak of the distribution occurs. The value must fulfill the condition left <= mode <= right.
rightfloat or array_like of floats
Upper limit, must be larger than left.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if left, mode, and right are all scalars. Otherwise, np.broadcast(left, mode, right).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized triangular distribution. See also Generator.triangular
which should be used for new code. Notes The probability density function for the triangular distribution is \[\begin{split}P(x;l, m, r) = \begin{cases} \frac{2(x-l)}{(r-l)(m-l)}& \text{for $l \leq x \leq m$},\\ \frac{2(r-x)}{(r-l)(r-m)}& \text{for $m \leq x \leq r$},\\ 0& \text{otherwise}. \end{cases}\end{split}\] The triangular distribution is often used in ill-defined problems where the underlying distribution is not known, but some knowledge of the limits and mode exists. Often it is used in simulations. References 1
Wikipedia, “Triangular distribution” https://en.wikipedia.org/wiki/Triangular_distribution Examples Draw values from the distribution and plot the histogram: >>> import matplotlib.pyplot as plt
>>> h = plt.hist(np.random.triangular(-3, 0, 8, 100000), bins=200,
... density=True)
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.triangular |
numpy.random.RandomState.uniform method random.RandomState.uniform(low=0.0, high=1.0, size=None)
Draw samples from a uniform distribution. Samples are uniformly distributed over the half-open interval [low, high) (includes low, but excludes high). In other words, any value within the given interval is equally likely to be drawn by uniform. Note New code should use the uniform method of a default_rng() instance instead; please see the Quick Start. Parameters
lowfloat or array_like of floats, optional
Lower boundary of the output interval. All values generated will be greater than or equal to low. The default value is 0.
highfloat or array_like of floats
Upper boundary of the output interval. All values generated will be less than or equal to high. The high limit may be included in the returned array of floats due to floating-point rounding in the equation low + (high-low) * random_sample(). The default value is 1.0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if low and high are both scalars. Otherwise, np.broadcast(low, high).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized uniform distribution. See also randint
Discrete uniform distribution, yielding integers. random_integers
Discrete uniform distribution over the closed interval [low, high]. random_sample
Floats uniformly distributed over [0, 1). random
Alias for random_sample. rand
Convenience function that accepts dimensions as input, e.g., rand(2,2) would generate a 2-by-2 array of floats, uniformly distributed over [0, 1). Generator.uniform
which should be used for new code. Notes The probability density function of the uniform distribution is \[p(x) = \frac{1}{b - a}\] anywhere within the interval [a, b), and zero elsewhere. When high == low, values of low will be returned. If high < low, the results are officially undefined and may eventually raise an error, i.e. do not rely on this function to behave when passed arguments satisfying that inequality condition. The high limit may be included in the returned array of floats due to floating-point rounding in the equation low + (high-low) * random_sample(). For example: >>> x = np.float32(5*0.99999999)
>>> x
5.0
Examples Draw samples from the distribution: >>> s = np.random.uniform(-1,0,1000)
All values are within the given interval: >>> np.all(s >= -1)
True
>>> np.all(s < 0)
True
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> count, bins, ignored = plt.hist(s, 15, density=True)
>>> plt.plot(bins, np.ones_like(bins), linewidth=2, color='r')
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.uniform |
numpy.random.RandomState.vonmises method random.RandomState.vonmises(mu, kappa, size=None)
Draw samples from a von Mises distribution. Samples are drawn from a von Mises distribution with specified mode (mu) and dispersion (kappa), on the interval [-pi, pi]. The von Mises distribution (also known as the circular normal distribution) is a continuous probability distribution on the unit circle. It may be thought of as the circular analogue of the normal distribution. Note New code should use the vonmises method of a default_rng() instance instead; please see the Quick Start. Parameters
mufloat or array_like of floats
Mode (“center”) of the distribution.
kappafloat or array_like of floats
Dispersion of the distribution, has to be >=0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if mu and kappa are both scalars. Otherwise, np.broadcast(mu, kappa).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized von Mises distribution. See also scipy.stats.vonmises
probability density function, distribution, or cumulative density function, etc. Generator.vonmises
which should be used for new code. Notes The probability density for the von Mises distribution is \[p(x) = \frac{e^{\kappa cos(x-\mu)}}{2\pi I_0(\kappa)},\] where \(\mu\) is the mode and \(\kappa\) the dispersion, and \(I_0(\kappa)\) is the modified Bessel function of order 0. The von Mises is named for Richard Edler von Mises, who was born in Austria-Hungary, in what is now the Ukraine. He fled to the United States in 1939 and became a professor at Harvard. He worked in probability theory, aerodynamics, fluid mechanics, and philosophy of science. References 1
Abramowitz, M. and Stegun, I. A. (Eds.). “Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing,” New York: Dover, 1972. 2
von Mises, R., “Mathematical Theory of Probability and Statistics”, New York: Academic Press, 1964. Examples Draw samples from the distribution: >>> mu, kappa = 0.0, 4.0 # mean and dispersion
>>> s = np.random.vonmises(mu, kappa, 1000)
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> from scipy.special import i0
>>> plt.hist(s, 50, density=True)
>>> x = np.linspace(-np.pi, np.pi, num=51)
>>> y = np.exp(kappa*np.cos(x-mu))/(2*np.pi*i0(kappa))
>>> plt.plot(x, y, linewidth=2, color='r')
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.vonmises |
numpy.random.RandomState.wald method random.RandomState.wald(mean, scale, size=None)
Draw samples from a Wald, or inverse Gaussian, distribution. As the scale approaches infinity, the distribution becomes more like a Gaussian. Some references claim that the Wald is an inverse Gaussian with mean equal to 1, but this is by no means universal. The inverse Gaussian distribution was first studied in relationship to Brownian motion. In 1956 M.C.K. Tweedie used the name inverse Gaussian because there is an inverse relationship between the time to cover a unit distance and distance covered in unit time. Note New code should use the wald method of a default_rng() instance instead; please see the Quick Start. Parameters
meanfloat or array_like of floats
Distribution mean, must be > 0.
scalefloat or array_like of floats
Scale parameter, must be > 0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if mean and scale are both scalars. Otherwise, np.broadcast(mean, scale).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Wald distribution. See also Generator.wald
which should be used for new code. Notes The probability density function for the Wald distribution is \[P(x;mean,scale) = \sqrt{\frac{scale}{2\pi x^3}}e^ \frac{-scale(x-mean)^2}{2\cdotp mean^2x}\] As noted above the inverse Gaussian distribution first arise from attempts to model Brownian motion. It is also a competitor to the Weibull for use in reliability modeling and modeling stock returns and interest rate processes. References 1
Brighton Webs Ltd., Wald Distribution, https://web.archive.org/web/20090423014010/http://www.brighton-webs.co.uk:80/distributions/wald.asp 2
Chhikara, Raj S., and Folks, J. Leroy, “The Inverse Gaussian Distribution: Theory : Methodology, and Applications”, CRC Press, 1988. 3
Wikipedia, “Inverse Gaussian distribution” https://en.wikipedia.org/wiki/Inverse_Gaussian_distribution Examples Draw values from the distribution and plot the histogram: >>> import matplotlib.pyplot as plt
>>> h = plt.hist(np.random.wald(3, 2, 100000), bins=200, density=True)
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.wald |
numpy.random.RandomState.weibull method random.RandomState.weibull(a, size=None)
Draw samples from a Weibull distribution. Draw samples from a 1-parameter Weibull distribution with the given shape parameter a. \[X = (-ln(U))^{1/a}\] Here, U is drawn from the uniform distribution over (0,1]. The more common 2-parameter Weibull, including a scale parameter \(\lambda\) is just \(X = \lambda(-ln(U))^{1/a}\). Note New code should use the weibull method of a default_rng() instance instead; please see the Quick Start. Parameters
afloat or array_like of floats
Shape parameter of the distribution. Must be nonnegative.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if a is a scalar. Otherwise, np.array(a).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Weibull distribution. See also scipy.stats.weibull_max
scipy.stats.weibull_min
scipy.stats.genextreme
gumbel
Generator.weibull
which should be used for new code. Notes The Weibull (or Type III asymptotic extreme value distribution for smallest values, SEV Type III, or Rosin-Rammler distribution) is one of a class of Generalized Extreme Value (GEV) distributions used in modeling extreme value problems. This class includes the Gumbel and Frechet distributions. The probability density for the Weibull distribution is \[p(x) = \frac{a} {\lambda}(\frac{x}{\lambda})^{a-1}e^{-(x/\lambda)^a},\] where \(a\) is the shape and \(\lambda\) the scale. The function has its peak (the mode) at \(\lambda(\frac{a-1}{a})^{1/a}\). When a = 1, the Weibull distribution reduces to the exponential distribution. References 1
Waloddi Weibull, Royal Technical University, Stockholm, 1939 “A Statistical Theory Of The Strength Of Materials”, Ingeniorsvetenskapsakademiens Handlingar Nr 151, 1939, Generalstabens Litografiska Anstalts Forlag, Stockholm. 2
Waloddi Weibull, “A Statistical Distribution Function of Wide Applicability”, Journal Of Applied Mechanics ASME Paper 1951. 3
Wikipedia, “Weibull distribution”, https://en.wikipedia.org/wiki/Weibull_distribution Examples Draw samples from the distribution: >>> a = 5. # shape
>>> s = np.random.weibull(a, 1000)
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> x = np.arange(1,100.)/50.
>>> def weib(x,n,a):
... return (a / n) * (x / n)**(a - 1) * np.exp(-(x / n)**a)
>>> count, bins, ignored = plt.hist(np.random.weibull(5.,1000))
>>> x = np.arange(1,100.)/50.
>>> scale = count.max()/weib(x, 1., 5.).max()
>>> plt.plot(x, weib(x, 1., 5.)*scale)
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.weibull |
numpy.random.RandomState.zipf method random.RandomState.zipf(a, size=None)
Draw samples from a Zipf distribution. Samples are drawn from a Zipf distribution with specified parameter a > 1. The Zipf distribution (also known as the zeta distribution) is a discrete probability distribution that satisfies Zipf’s law: the frequency of an item is inversely proportional to its rank in a frequency table. Note New code should use the zipf method of a default_rng() instance instead; please see the Quick Start. Parameters
afloat or array_like of floats
Distribution parameter. Must be greater than 1.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if a is a scalar. Otherwise, np.array(a).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Zipf distribution. See also scipy.stats.zipf
probability density function, distribution, or cumulative density function, etc. Generator.zipf
which should be used for new code. Notes The probability density for the Zipf distribution is \[p(k) = \frac{k^{-a}}{\zeta(a)},\] for integers \(k \geq 1\), where \(\zeta\) is the Riemann Zeta function. It is named for the American linguist George Kingsley Zipf, who noted that the frequency of any word in a sample of a language is inversely proportional to its rank in the frequency table. References 1
Zipf, G. K., “Selected Studies of the Principle of Relative Frequency in Language,” Cambridge, MA: Harvard Univ. Press, 1932. Examples Draw samples from the distribution: >>> a = 4.0
>>> n = 20000
>>> s = np.random.zipf(a, n)
Display the histogram of the samples, along with the expected histogram based on the probability density function: >>> import matplotlib.pyplot as plt
>>> from scipy.special import zeta
bincount provides a fast histogram for small integers. >>> count = np.bincount(s)
>>> k = np.arange(1, s.max() + 1)
>>> plt.bar(k, count[1:], alpha=0.5, label='sample count')
>>> plt.plot(k, n*(k**-a)/zeta(a), 'k.-', alpha=0.5,
... label='expected count')
>>> plt.semilogy()
>>> plt.grid(alpha=0.4)
>>> plt.legend()
>>> plt.title(f'Zipf sample, a={a}, size={n}')
>>> plt.show() | numpy.reference.random.generated.numpy.random.randomstate.zipf |
numpy.random.ranf random.ranf()
This is an alias of random_sample. See random_sample for the complete documentation. | numpy.reference.random.generated.numpy.random.ranf |
numpy.random.rayleigh random.rayleigh(scale=1.0, size=None)
Draw samples from a Rayleigh distribution. The \(\chi\) and Weibull distributions are generalizations of the Rayleigh. Note New code should use the rayleigh method of a default_rng() instance instead; please see the Quick Start. Parameters
scalefloat or array_like of floats, optional
Scale, also equals the mode. Must be non-negative. Default is 1.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if scale is a scalar. Otherwise, np.array(scale).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Rayleigh distribution. See also Generator.rayleigh
which should be used for new code. Notes The probability density function for the Rayleigh distribution is \[P(x;scale) = \frac{x}{scale^2}e^{\frac{-x^2}{2 \cdotp scale^2}}\] The Rayleigh distribution would arise, for example, if the East and North components of the wind velocity had identical zero-mean Gaussian distributions. Then the wind speed would have a Rayleigh distribution. References 1
Brighton Webs Ltd., “Rayleigh Distribution,” https://web.archive.org/web/20090514091424/http://brighton-webs.co.uk:80/distributions/rayleigh.asp 2
Wikipedia, “Rayleigh distribution” https://en.wikipedia.org/wiki/Rayleigh_distribution Examples Draw values from the distribution and plot the histogram >>> from matplotlib.pyplot import hist
>>> values = hist(np.random.rayleigh(3, 100000), bins=200, density=True)
Wave heights tend to follow a Rayleigh distribution. If the mean wave height is 1 meter, what fraction of waves are likely to be larger than 3 meters? >>> meanvalue = 1
>>> modevalue = np.sqrt(2 / np.pi) * meanvalue
>>> s = np.random.rayleigh(modevalue, 1000000)
The percentage of waves larger than 3 meters is: >>> 100.*sum(s>3)/1000000.
0.087300000000000003 # random | numpy.reference.random.generated.numpy.random.rayleigh |
numpy.random.sample random.sample()
This is an alias of random_sample. See random_sample for the complete documentation. | numpy.reference.random.generated.numpy.random.sample |
numpy.random.seed random.seed(self, seed=None)
Reseed a legacy MT19937 BitGenerator Notes This is a convenience, legacy function. The best practice is to not reseed a BitGenerator, rather to recreate a new one. This method is here for legacy reasons. This example demonstrates best practice. >>> from numpy.random import MT19937
>>> from numpy.random import RandomState, SeedSequence
>>> rs = RandomState(MT19937(SeedSequence(123456789)))
# Later, you want to restart the stream
>>> rs = RandomState(MT19937(SeedSequence(987654321))) | numpy.reference.random.generated.numpy.random.seed |
numpy.random.SeedSequence.entropy attribute random.SeedSequence.entropy | numpy.reference.random.bit_generators.generated.numpy.random.seedsequence.entropy |
numpy.random.SeedSequence.generate_state method random.SeedSequence.generate_state(n_words, dtype=np.uint32)
Return the requested number of words for PRNG seeding. A BitGenerator should call this method in its constructor with an appropriate n_words parameter to properly seed itself. Parameters
n_wordsint
dtypenp.uint32 or np.uint64, optional
The size of each word. This should only be either uint32 or uint64. Strings (‘uint32’, ‘uint64’) are fine. Note that requesting uint64 will draw twice as many bits as uint32 for the same n_words. This is a convenience for BitGenerator`s that express their states as `uint64 arrays. Returns
stateuint32 or uint64 array, shape=(n_words,) | numpy.reference.random.bit_generators.generated.numpy.random.seedsequence.generate_state |
numpy.random.SeedSequence.spawn method random.SeedSequence.spawn(n_children)
Spawn a number of child SeedSequence s by extending the spawn_key. Parameters
n_childrenint
Returns
seqslist of SeedSequence s | numpy.reference.random.bit_generators.generated.numpy.random.seedsequence.spawn |
numpy.random.SeedSequence.spawn_key attribute random.SeedSequence.spawn_key | numpy.reference.random.bit_generators.generated.numpy.random.seedsequence.spawn_key |
numpy.random.set_state random.set_state(state)
Set the internal state of the generator from a tuple. For use if one has reason to manually (re-)set the internal state of the bit generator used by the RandomState instance. By default, RandomState uses the “Mersenne Twister”[1] pseudo-random number generating algorithm. Parameters
state{tuple(str, ndarray of 624 uints, int, int, float), dict}
The state tuple has the following items: the string ‘MT19937’, specifying the Mersenne Twister algorithm. a 1-D array of 624 unsigned integers keys. an integer pos. an integer has_gauss. a float cached_gaussian. If state is a dictionary, it is directly set using the BitGenerators state property. Returns
outNone
Returns ‘None’ on success. See also get_state
Notes set_state and get_state are not needed to work with any of the random distributions in NumPy. If the internal state is manually altered, the user should know exactly what he/she is doing. For backwards compatibility, the form (str, array of 624 uints, int) is also accepted although it is missing some information about the cached Gaussian value: state = ('MT19937', keys, pos). References 1
M. Matsumoto and T. Nishimura, “Mersenne Twister: A 623-dimensionally equidistributed uniform pseudorandom number generator,” ACM Trans. on Modeling and Computer Simulation, Vol. 8, No. 1, pp. 3-30, Jan. 1998. | numpy.reference.random.generated.numpy.random.set_state |
numpy.random.SFC64.cffi attribute random.SFC64.cffi
CFFI interface Returns
interfacenamedtuple
Named tuple containing CFFI wrapper state_address - Memory address of the state struct state - pointer to the state struct next_uint64 - function pointer to produce 64 bit integers next_uint32 - function pointer to produce 32 bit integers next_double - function pointer to produce doubles bitgen - pointer to the bit generator struct | numpy.reference.random.bit_generators.generated.numpy.random.sfc64.cffi |
numpy.random.SFC64.ctypes attribute random.SFC64.ctypes
ctypes interface Returns
interfacenamedtuple
Named tuple containing ctypes wrapper state_address - Memory address of the state struct state - pointer to the state struct next_uint64 - function pointer to produce 64 bit integers next_uint32 - function pointer to produce 32 bit integers next_double - function pointer to produce doubles bitgen - pointer to the bit generator struct | numpy.reference.random.bit_generators.generated.numpy.random.sfc64.ctypes |
numpy.random.SFC64.state attribute random.SFC64.state
Get or set the PRNG state Returns
statedict
Dictionary containing the information required to describe the state of the PRNG | numpy.reference.random.bit_generators.generated.numpy.random.sfc64.state |
numpy.random.shuffle random.shuffle(x)
Modify a sequence in-place by shuffling its contents. This function only shuffles the array along the first axis of a multi-dimensional array. The order of sub-arrays is changed but their contents remains the same. Note New code should use the shuffle method of a default_rng() instance instead; please see the Quick Start. Parameters
xndarray or MutableSequence
The array, list or mutable sequence to be shuffled. Returns
None
See also Generator.shuffle
which should be used for new code. Examples >>> arr = np.arange(10)
>>> np.random.shuffle(arr)
>>> arr
[1 7 5 2 9 4 3 6 0 8] # random
Multi-dimensional arrays are only shuffled along the first axis: >>> arr = np.arange(9).reshape((3, 3))
>>> np.random.shuffle(arr)
>>> arr
array([[3, 4, 5], # random
[6, 7, 8],
[0, 1, 2]]) | numpy.reference.random.generated.numpy.random.shuffle |
numpy.random.standard_cauchy random.standard_cauchy(size=None)
Draw samples from a standard Cauchy distribution with mode = 0. Also known as the Lorentz distribution. Note New code should use the standard_cauchy method of a default_rng() instance instead; please see the Quick Start. Parameters
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. Default is None, in which case a single value is returned. Returns
samplesndarray or scalar
The drawn samples. See also Generator.standard_cauchy
which should be used for new code. Notes The probability density function for the full Cauchy distribution is \[P(x; x_0, \gamma) = \frac{1}{\pi \gamma \bigl[ 1+ (\frac{x-x_0}{\gamma})^2 \bigr] }\] and the Standard Cauchy distribution just sets \(x_0=0\) and \(\gamma=1\) The Cauchy distribution arises in the solution to the driven harmonic oscillator problem, and also describes spectral line broadening. It also describes the distribution of values at which a line tilted at a random angle will cut the x axis. When studying hypothesis tests that assume normality, seeing how the tests perform on data from a Cauchy distribution is a good indicator of their sensitivity to a heavy-tailed distribution, since the Cauchy looks very much like a Gaussian distribution, but with heavier tails. References 1
NIST/SEMATECH e-Handbook of Statistical Methods, “Cauchy Distribution”, https://www.itl.nist.gov/div898/handbook/eda/section3/eda3663.htm 2
Weisstein, Eric W. “Cauchy Distribution.” From MathWorld–A Wolfram Web Resource. http://mathworld.wolfram.com/CauchyDistribution.html 3
Wikipedia, “Cauchy distribution” https://en.wikipedia.org/wiki/Cauchy_distribution Examples Draw samples and plot the distribution: >>> import matplotlib.pyplot as plt
>>> s = np.random.standard_cauchy(1000000)
>>> s = s[(s>-25) & (s<25)] # truncate distribution so it plots well
>>> plt.hist(s, bins=100)
>>> plt.show() | numpy.reference.random.generated.numpy.random.standard_cauchy |
numpy.random.standard_exponential random.standard_exponential(size=None)
Draw samples from the standard exponential distribution. standard_exponential is identical to the exponential distribution with a scale parameter of 1. Note New code should use the standard_exponential method of a default_rng() instance instead; please see the Quick Start. Parameters
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. Default is None, in which case a single value is returned. Returns
outfloat or ndarray
Drawn samples. See also Generator.standard_exponential
which should be used for new code. Examples Output a 3x8000 array: >>> n = np.random.standard_exponential((3, 8000)) | numpy.reference.random.generated.numpy.random.standard_exponential |
numpy.random.standard_gamma random.standard_gamma(shape, size=None)
Draw samples from a standard Gamma distribution. Samples are drawn from a Gamma distribution with specified parameters, shape (sometimes designated “k”) and scale=1. Note New code should use the standard_gamma method of a default_rng() instance instead; please see the Quick Start. Parameters
shapefloat or array_like of floats
Parameter, must be non-negative.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if shape is a scalar. Otherwise, np.array(shape).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized standard gamma distribution. See also scipy.stats.gamma
probability density function, distribution or cumulative density function, etc. Generator.standard_gamma
which should be used for new code. Notes The probability density for the Gamma distribution is \[p(x) = x^{k-1}\frac{e^{-x/\theta}}{\theta^k\Gamma(k)},\] where \(k\) is the shape and \(\theta\) the scale, and \(\Gamma\) is the Gamma function. The Gamma distribution is often used to model the times to failure of electronic components, and arises naturally in processes for which the waiting times between Poisson distributed events are relevant. References 1
Weisstein, Eric W. “Gamma Distribution.” From MathWorld–A Wolfram Web Resource. http://mathworld.wolfram.com/GammaDistribution.html 2
Wikipedia, “Gamma distribution”, https://en.wikipedia.org/wiki/Gamma_distribution Examples Draw samples from the distribution: >>> shape, scale = 2., 1. # mean and width
>>> s = np.random.standard_gamma(shape, 1000000)
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> import scipy.special as sps
>>> count, bins, ignored = plt.hist(s, 50, density=True)
>>> y = bins**(shape-1) * ((np.exp(-bins/scale))/
... (sps.gamma(shape) * scale**shape))
>>> plt.plot(bins, y, linewidth=2, color='r')
>>> plt.show() | numpy.reference.random.generated.numpy.random.standard_gamma |
numpy.random.standard_normal random.standard_normal(size=None)
Draw samples from a standard Normal distribution (mean=0, stdev=1). Note New code should use the standard_normal method of a default_rng() instance instead; please see the Quick Start. Parameters
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. Default is None, in which case a single value is returned. Returns
outfloat or ndarray
A floating-point array of shape size of drawn samples, or a single sample if size was not specified. See also normal
Equivalent function with additional loc and scale arguments for setting the mean and standard deviation. Generator.standard_normal
which should be used for new code. Notes For random samples from \(N(\mu, \sigma^2)\), use one of: mu + sigma * np.random.standard_normal(size=...)
np.random.normal(mu, sigma, size=...)
Examples >>> np.random.standard_normal()
2.1923875335537315 #random
>>> s = np.random.standard_normal(8000)
>>> s
array([ 0.6888893 , 0.78096262, -0.89086505, ..., 0.49876311, # random
-0.38672696, -0.4685006 ]) # random
>>> s.shape
(8000,)
>>> s = np.random.standard_normal(size=(3, 4, 2))
>>> s.shape
(3, 4, 2)
Two-by-four array of samples from \(N(3, 6.25)\): >>> 3 + 2.5 * np.random.standard_normal(size=(2, 4))
array([[-4.49401501, 4.00950034, -1.81814867, 7.29718677], # random
[ 0.39924804, 4.68456316, 4.99394529, 4.84057254]]) # random | numpy.reference.random.generated.numpy.random.standard_normal |
numpy.random.standard_t random.standard_t(df, size=None)
Draw samples from a standard Student’s t distribution with df degrees of freedom. A special case of the hyperbolic distribution. As df gets large, the result resembles that of the standard normal distribution (standard_normal). Note New code should use the standard_t method of a default_rng() instance instead; please see the Quick Start. Parameters
dffloat or array_like of floats
Degrees of freedom, must be > 0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if df is a scalar. Otherwise, np.array(df).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized standard Student’s t distribution. See also Generator.standard_t
which should be used for new code. Notes The probability density function for the t distribution is \[P(x, df) = \frac{\Gamma(\frac{df+1}{2})}{\sqrt{\pi df} \Gamma(\frac{df}{2})}\Bigl( 1+\frac{x^2}{df} \Bigr)^{-(df+1)/2}\] The t test is based on an assumption that the data come from a Normal distribution. The t test provides a way to test whether the sample mean (that is the mean calculated from the data) is a good estimate of the true mean. The derivation of the t-distribution was first published in 1908 by William Gosset while working for the Guinness Brewery in Dublin. Due to proprietary issues, he had to publish under a pseudonym, and so he used the name Student. References 1
Dalgaard, Peter, “Introductory Statistics With R”, Springer, 2002. 2
Wikipedia, “Student’s t-distribution” https://en.wikipedia.org/wiki/Student’s_t-distribution Examples From Dalgaard page 83 [1], suppose the daily energy intake for 11 women in kilojoules (kJ) is: >>> intake = np.array([5260., 5470, 5640, 6180, 6390, 6515, 6805, 7515, \
... 7515, 8230, 8770])
Does their energy intake deviate systematically from the recommended value of 7725 kJ? Our null hypothesis will be the absence of deviation, and the alternate hypothesis will be the presence of an effect that could be either positive or negative, hence making our test 2-tailed. Because we are estimating the mean and we have N=11 values in our sample, we have N-1=10 degrees of freedom. We set our significance level to 95% and compute the t statistic using the empirical mean and empirical standard deviation of our intake. We use a ddof of 1 to base the computation of our empirical standard deviation on an unbiased estimate of the variance (note: the final estimate is not unbiased due to the concave nature of the square root). >>> np.mean(intake)
6753.636363636364
>>> intake.std(ddof=1)
1142.1232221373727
>>> t = (np.mean(intake)-7725)/(intake.std(ddof=1)/np.sqrt(len(intake)))
>>> t
-2.8207540608310198
We draw 1000000 samples from Student’s t distribution with the adequate degrees of freedom. >>> import matplotlib.pyplot as plt
>>> s = np.random.standard_t(10, size=1000000)
>>> h = plt.hist(s, bins=100, density=True)
Does our t statistic land in one of the two critical regions found at both tails of the distribution? >>> np.sum(np.abs(t) < np.abs(s)) / float(len(s))
0.018318 #random < 0.05, statistic is in critical region
The probability value for this 2-tailed test is about 1.83%, which is lower than the 5% pre-determined significance threshold. Therefore, the probability of observing values as extreme as our intake conditionally on the null hypothesis being true is too low, and we reject the null hypothesis of no deviation. | numpy.reference.random.generated.numpy.random.standard_t |
numpy.random.triangular random.triangular(left, mode, right, size=None)
Draw samples from the triangular distribution over the interval [left, right]. The triangular distribution is a continuous probability distribution with lower limit left, peak at mode, and upper limit right. Unlike the other distributions, these parameters directly define the shape of the pdf. Note New code should use the triangular method of a default_rng() instance instead; please see the Quick Start. Parameters
leftfloat or array_like of floats
Lower limit.
modefloat or array_like of floats
The value where the peak of the distribution occurs. The value must fulfill the condition left <= mode <= right.
rightfloat or array_like of floats
Upper limit, must be larger than left.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if left, mode, and right are all scalars. Otherwise, np.broadcast(left, mode, right).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized triangular distribution. See also Generator.triangular
which should be used for new code. Notes The probability density function for the triangular distribution is \[\begin{split}P(x;l, m, r) = \begin{cases} \frac{2(x-l)}{(r-l)(m-l)}& \text{for $l \leq x \leq m$},\\ \frac{2(r-x)}{(r-l)(r-m)}& \text{for $m \leq x \leq r$},\\ 0& \text{otherwise}. \end{cases}\end{split}\] The triangular distribution is often used in ill-defined problems where the underlying distribution is not known, but some knowledge of the limits and mode exists. Often it is used in simulations. References 1
Wikipedia, “Triangular distribution” https://en.wikipedia.org/wiki/Triangular_distribution Examples Draw values from the distribution and plot the histogram: >>> import matplotlib.pyplot as plt
>>> h = plt.hist(np.random.triangular(-3, 0, 8, 100000), bins=200,
... density=True)
>>> plt.show() | numpy.reference.random.generated.numpy.random.triangular |
numpy.random.uniform random.uniform(low=0.0, high=1.0, size=None)
Draw samples from a uniform distribution. Samples are uniformly distributed over the half-open interval [low, high) (includes low, but excludes high). In other words, any value within the given interval is equally likely to be drawn by uniform. Note New code should use the uniform method of a default_rng() instance instead; please see the Quick Start. Parameters
lowfloat or array_like of floats, optional
Lower boundary of the output interval. All values generated will be greater than or equal to low. The default value is 0.
highfloat or array_like of floats
Upper boundary of the output interval. All values generated will be less than or equal to high. The high limit may be included in the returned array of floats due to floating-point rounding in the equation low + (high-low) * random_sample(). The default value is 1.0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if low and high are both scalars. Otherwise, np.broadcast(low, high).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized uniform distribution. See also randint
Discrete uniform distribution, yielding integers. random_integers
Discrete uniform distribution over the closed interval [low, high]. random_sample
Floats uniformly distributed over [0, 1). random
Alias for random_sample. rand
Convenience function that accepts dimensions as input, e.g., rand(2,2) would generate a 2-by-2 array of floats, uniformly distributed over [0, 1). Generator.uniform
which should be used for new code. Notes The probability density function of the uniform distribution is \[p(x) = \frac{1}{b - a}\] anywhere within the interval [a, b), and zero elsewhere. When high == low, values of low will be returned. If high < low, the results are officially undefined and may eventually raise an error, i.e. do not rely on this function to behave when passed arguments satisfying that inequality condition. The high limit may be included in the returned array of floats due to floating-point rounding in the equation low + (high-low) * random_sample(). For example: >>> x = np.float32(5*0.99999999)
>>> x
5.0
Examples Draw samples from the distribution: >>> s = np.random.uniform(-1,0,1000)
All values are within the given interval: >>> np.all(s >= -1)
True
>>> np.all(s < 0)
True
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> count, bins, ignored = plt.hist(s, 15, density=True)
>>> plt.plot(bins, np.ones_like(bins), linewidth=2, color='r')
>>> plt.show() | numpy.reference.random.generated.numpy.random.uniform |
numpy.random.vonmises random.vonmises(mu, kappa, size=None)
Draw samples from a von Mises distribution. Samples are drawn from a von Mises distribution with specified mode (mu) and dispersion (kappa), on the interval [-pi, pi]. The von Mises distribution (also known as the circular normal distribution) is a continuous probability distribution on the unit circle. It may be thought of as the circular analogue of the normal distribution. Note New code should use the vonmises method of a default_rng() instance instead; please see the Quick Start. Parameters
mufloat or array_like of floats
Mode (“center”) of the distribution.
kappafloat or array_like of floats
Dispersion of the distribution, has to be >=0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if mu and kappa are both scalars. Otherwise, np.broadcast(mu, kappa).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized von Mises distribution. See also scipy.stats.vonmises
probability density function, distribution, or cumulative density function, etc. Generator.vonmises
which should be used for new code. Notes The probability density for the von Mises distribution is \[p(x) = \frac{e^{\kappa cos(x-\mu)}}{2\pi I_0(\kappa)},\] where \(\mu\) is the mode and \(\kappa\) the dispersion, and \(I_0(\kappa)\) is the modified Bessel function of order 0. The von Mises is named for Richard Edler von Mises, who was born in Austria-Hungary, in what is now the Ukraine. He fled to the United States in 1939 and became a professor at Harvard. He worked in probability theory, aerodynamics, fluid mechanics, and philosophy of science. References 1
Abramowitz, M. and Stegun, I. A. (Eds.). “Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing,” New York: Dover, 1972. 2
von Mises, R., “Mathematical Theory of Probability and Statistics”, New York: Academic Press, 1964. Examples Draw samples from the distribution: >>> mu, kappa = 0.0, 4.0 # mean and dispersion
>>> s = np.random.vonmises(mu, kappa, 1000)
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> from scipy.special import i0
>>> plt.hist(s, 50, density=True)
>>> x = np.linspace(-np.pi, np.pi, num=51)
>>> y = np.exp(kappa*np.cos(x-mu))/(2*np.pi*i0(kappa))
>>> plt.plot(x, y, linewidth=2, color='r')
>>> plt.show() | numpy.reference.random.generated.numpy.random.vonmises |
numpy.random.wald random.wald(mean, scale, size=None)
Draw samples from a Wald, or inverse Gaussian, distribution. As the scale approaches infinity, the distribution becomes more like a Gaussian. Some references claim that the Wald is an inverse Gaussian with mean equal to 1, but this is by no means universal. The inverse Gaussian distribution was first studied in relationship to Brownian motion. In 1956 M.C.K. Tweedie used the name inverse Gaussian because there is an inverse relationship between the time to cover a unit distance and distance covered in unit time. Note New code should use the wald method of a default_rng() instance instead; please see the Quick Start. Parameters
meanfloat or array_like of floats
Distribution mean, must be > 0.
scalefloat or array_like of floats
Scale parameter, must be > 0.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if mean and scale are both scalars. Otherwise, np.broadcast(mean, scale).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Wald distribution. See also Generator.wald
which should be used for new code. Notes The probability density function for the Wald distribution is \[P(x;mean,scale) = \sqrt{\frac{scale}{2\pi x^3}}e^ \frac{-scale(x-mean)^2}{2\cdotp mean^2x}\] As noted above the inverse Gaussian distribution first arise from attempts to model Brownian motion. It is also a competitor to the Weibull for use in reliability modeling and modeling stock returns and interest rate processes. References 1
Brighton Webs Ltd., Wald Distribution, https://web.archive.org/web/20090423014010/http://www.brighton-webs.co.uk:80/distributions/wald.asp 2
Chhikara, Raj S., and Folks, J. Leroy, “The Inverse Gaussian Distribution: Theory : Methodology, and Applications”, CRC Press, 1988. 3
Wikipedia, “Inverse Gaussian distribution” https://en.wikipedia.org/wiki/Inverse_Gaussian_distribution Examples Draw values from the distribution and plot the histogram: >>> import matplotlib.pyplot as plt
>>> h = plt.hist(np.random.wald(3, 2, 100000), bins=200, density=True)
>>> plt.show() | numpy.reference.random.generated.numpy.random.wald |
numpy.random.weibull random.weibull(a, size=None)
Draw samples from a Weibull distribution. Draw samples from a 1-parameter Weibull distribution with the given shape parameter a. \[X = (-ln(U))^{1/a}\] Here, U is drawn from the uniform distribution over (0,1]. The more common 2-parameter Weibull, including a scale parameter \(\lambda\) is just \(X = \lambda(-ln(U))^{1/a}\). Note New code should use the weibull method of a default_rng() instance instead; please see the Quick Start. Parameters
afloat or array_like of floats
Shape parameter of the distribution. Must be nonnegative.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if a is a scalar. Otherwise, np.array(a).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Weibull distribution. See also scipy.stats.weibull_max
scipy.stats.weibull_min
scipy.stats.genextreme
gumbel
Generator.weibull
which should be used for new code. Notes The Weibull (or Type III asymptotic extreme value distribution for smallest values, SEV Type III, or Rosin-Rammler distribution) is one of a class of Generalized Extreme Value (GEV) distributions used in modeling extreme value problems. This class includes the Gumbel and Frechet distributions. The probability density for the Weibull distribution is \[p(x) = \frac{a} {\lambda}(\frac{x}{\lambda})^{a-1}e^{-(x/\lambda)^a},\] where \(a\) is the shape and \(\lambda\) the scale. The function has its peak (the mode) at \(\lambda(\frac{a-1}{a})^{1/a}\). When a = 1, the Weibull distribution reduces to the exponential distribution. References 1
Waloddi Weibull, Royal Technical University, Stockholm, 1939 “A Statistical Theory Of The Strength Of Materials”, Ingeniorsvetenskapsakademiens Handlingar Nr 151, 1939, Generalstabens Litografiska Anstalts Forlag, Stockholm. 2
Waloddi Weibull, “A Statistical Distribution Function of Wide Applicability”, Journal Of Applied Mechanics ASME Paper 1951. 3
Wikipedia, “Weibull distribution”, https://en.wikipedia.org/wiki/Weibull_distribution Examples Draw samples from the distribution: >>> a = 5. # shape
>>> s = np.random.weibull(a, 1000)
Display the histogram of the samples, along with the probability density function: >>> import matplotlib.pyplot as plt
>>> x = np.arange(1,100.)/50.
>>> def weib(x,n,a):
... return (a / n) * (x / n)**(a - 1) * np.exp(-(x / n)**a)
>>> count, bins, ignored = plt.hist(np.random.weibull(5.,1000))
>>> x = np.arange(1,100.)/50.
>>> scale = count.max()/weib(x, 1., 5.).max()
>>> plt.plot(x, weib(x, 1., 5.)*scale)
>>> plt.show() | numpy.reference.random.generated.numpy.random.weibull |
numpy.random.zipf random.zipf(a, size=None)
Draw samples from a Zipf distribution. Samples are drawn from a Zipf distribution with specified parameter a > 1. The Zipf distribution (also known as the zeta distribution) is a discrete probability distribution that satisfies Zipf’s law: the frequency of an item is inversely proportional to its rank in a frequency table. Note New code should use the zipf method of a default_rng() instance instead; please see the Quick Start. Parameters
afloat or array_like of floats
Distribution parameter. Must be greater than 1.
sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g., (m, n, k), then m * n * k samples are drawn. If size is None (default), a single value is returned if a is a scalar. Otherwise, np.array(a).size samples are drawn. Returns
outndarray or scalar
Drawn samples from the parameterized Zipf distribution. See also scipy.stats.zipf
probability density function, distribution, or cumulative density function, etc. Generator.zipf
which should be used for new code. Notes The probability density for the Zipf distribution is \[p(k) = \frac{k^{-a}}{\zeta(a)},\] for integers \(k \geq 1\), where \(\zeta\) is the Riemann Zeta function. It is named for the American linguist George Kingsley Zipf, who noted that the frequency of any word in a sample of a language is inversely proportional to its rank in the frequency table. References 1
Zipf, G. K., “Selected Studies of the Principle of Relative Frequency in Language,” Cambridge, MA: Harvard Univ. Press, 1932. Examples Draw samples from the distribution: >>> a = 4.0
>>> n = 20000
>>> s = np.random.zipf(a, n)
Display the histogram of the samples, along with the expected histogram based on the probability density function: >>> import matplotlib.pyplot as plt
>>> from scipy.special import zeta
bincount provides a fast histogram for small integers. >>> count = np.bincount(s)
>>> k = np.arange(1, s.max() + 1)
>>> plt.bar(k, count[1:], alpha=0.5, label='sample count')
>>> plt.plot(k, n*(k**-a)/zeta(a), 'k.-', alpha=0.5,
... label='expected count')
>>> plt.semilogy()
>>> plt.grid(alpha=0.4)
>>> plt.legend()
>>> plt.title(f'Zipf sample, a={a}, size={n}')
>>> plt.show() | numpy.reference.random.generated.numpy.random.zipf |
numpy.recarray.all method recarray.all(axis=None, out=None, keepdims=False, *, where=True)
Returns True if all elements evaluate to True. Refer to numpy.all for full documentation. See also numpy.all
equivalent function | numpy.reference.generated.numpy.recarray.all |
numpy.recarray.any method recarray.any(axis=None, out=None, keepdims=False, *, where=True)
Returns True if any of the elements of a evaluate to True. Refer to numpy.any for full documentation. See also numpy.any
equivalent function | numpy.reference.generated.numpy.recarray.any |
numpy.recarray.argmax method recarray.argmax(axis=None, out=None)
Return indices of the maximum values along the given axis. Refer to numpy.argmax for full documentation. See also numpy.argmax
equivalent function | numpy.reference.generated.numpy.recarray.argmax |
numpy.recarray.argmin method recarray.argmin(axis=None, out=None)
Return indices of the minimum values along the given axis. Refer to numpy.argmin for detailed documentation. See also numpy.argmin
equivalent function | numpy.reference.generated.numpy.recarray.argmin |
numpy.recarray.argpartition method recarray.argpartition(kth, axis=- 1, kind='introselect', order=None)
Returns the indices that would partition this array. Refer to numpy.argpartition for full documentation. New in version 1.8.0. See also numpy.argpartition
equivalent function | numpy.reference.generated.numpy.recarray.argpartition |
numpy.recarray.argsort method recarray.argsort(axis=- 1, kind=None, order=None)
Returns the indices that would sort this array. Refer to numpy.argsort for full documentation. See also numpy.argsort
equivalent function | numpy.reference.generated.numpy.recarray.argsort |
numpy.recarray.astype method recarray.astype(dtype, order='K', casting='unsafe', subok=True, copy=True)
Copy of the array, cast to a specified type. Parameters
dtypestr or dtype
Typecode or data-type to which the array is cast.
order{‘C’, ‘F’, ‘A’, ‘K’}, optional
Controls the memory layout order of the result. ‘C’ means C order, ‘F’ means Fortran order, ‘A’ means ‘F’ order if all the arrays are Fortran contiguous, ‘C’ order otherwise, and ‘K’ means as close to the order the array elements appear in memory as possible. Default is ‘K’.
casting{‘no’, ‘equiv’, ‘safe’, ‘same_kind’, ‘unsafe’}, optional
Controls what kind of data casting may occur. Defaults to ‘unsafe’ for backwards compatibility. ‘no’ means the data types should not be cast at all. ‘equiv’ means only byte-order changes are allowed. ‘safe’ means only casts which can preserve values are allowed. ‘same_kind’ means only safe casts or casts within a kind, like float64 to float32, are allowed. ‘unsafe’ means any data conversions may be done.
subokbool, optional
If True, then sub-classes will be passed-through (default), otherwise the returned array will be forced to be a base-class array.
copybool, optional
By default, astype always returns a newly allocated array. If this is set to false, and the dtype, order, and subok requirements are satisfied, the input array is returned instead of a copy. Returns
arr_tndarray
Unless copy is False and the other conditions for returning the input array are satisfied (see description for copy input parameter), arr_t is a new array of the same shape as the input array, with dtype, order given by dtype, order. Raises
ComplexWarning
When casting from complex to float or int. To avoid this, one should use a.real.astype(t). Notes Changed in version 1.17.0: Casting between a simple data type and a structured one is possible only for “unsafe” casting. Casting to multiple fields is allowed, but casting from multiple fields is not. Changed in version 1.9.0: Casting from numeric to string types in ‘safe’ casting mode requires that the string dtype length is long enough to store the max integer/float value converted. Examples >>> x = np.array([1, 2, 2.5])
>>> x
array([1. , 2. , 2.5])
>>> x.astype(int)
array([1, 2, 2]) | numpy.reference.generated.numpy.recarray.astype |
numpy.recarray.base attribute recarray.base
Base object if memory is from some other object. Examples The base of an array that owns its memory is None: >>> x = np.array([1,2,3,4])
>>> x.base is None
True
Slicing creates a view, whose memory is shared with x: >>> y = x[2:]
>>> y.base is x
True | numpy.reference.generated.numpy.recarray.base |
numpy.recarray.byteswap method recarray.byteswap(inplace=False)
Swap the bytes of the array elements Toggle between low-endian and big-endian data representation by returning a byteswapped array, optionally swapped in-place. Arrays of byte-strings are not swapped. The real and imaginary parts of a complex number are swapped individually. Parameters
inplacebool, optional
If True, swap bytes in-place, default is False. Returns
outndarray
The byteswapped array. If inplace is True, this is a view to self. Examples >>> A = np.array([1, 256, 8755], dtype=np.int16)
>>> list(map(hex, A))
['0x1', '0x100', '0x2233']
>>> A.byteswap(inplace=True)
array([ 256, 1, 13090], dtype=int16)
>>> list(map(hex, A))
['0x100', '0x1', '0x3322']
Arrays of byte-strings are not swapped >>> A = np.array([b'ceg', b'fac'])
>>> A.byteswap()
array([b'ceg', b'fac'], dtype='|S3')
A.newbyteorder().byteswap() produces an array with the same values
but different representation in memory >>> A = np.array([1, 2, 3])
>>> A.view(np.uint8)
array([1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0,
0, 0], dtype=uint8)
>>> A.newbyteorder().byteswap(inplace=True)
array([1, 2, 3])
>>> A.view(np.uint8)
array([0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0,
0, 3], dtype=uint8) | numpy.reference.generated.numpy.recarray.byteswap |
numpy.recarray.choose method recarray.choose(choices, out=None, mode='raise')
Use an index array to construct a new array from a set of choices. Refer to numpy.choose for full documentation. See also numpy.choose
equivalent function | numpy.reference.generated.numpy.recarray.choose |
numpy.recarray.clip method recarray.clip(min=None, max=None, out=None, **kwargs)
Return an array whose values are limited to [min, max]. One of max or min must be given. Refer to numpy.clip for full documentation. See also numpy.clip
equivalent function | numpy.reference.generated.numpy.recarray.clip |
numpy.recarray.compress method recarray.compress(condition, axis=None, out=None)
Return selected slices of this array along given axis. Refer to numpy.compress for full documentation. See also numpy.compress
equivalent function | numpy.reference.generated.numpy.recarray.compress |
numpy.recarray.conj method recarray.conj()
Complex-conjugate all elements. Refer to numpy.conjugate for full documentation. See also numpy.conjugate
equivalent function | numpy.reference.generated.numpy.recarray.conj |
numpy.recarray.conjugate method recarray.conjugate()
Return the complex conjugate, element-wise. Refer to numpy.conjugate for full documentation. See also numpy.conjugate
equivalent function | numpy.reference.generated.numpy.recarray.conjugate |
numpy.recarray.copy method recarray.copy(order='C')
Return a copy of the array. Parameters
order{‘C’, ‘F’, ‘A’, ‘K’}, optional
Controls the memory layout of the copy. ‘C’ means C-order, ‘F’ means F-order, ‘A’ means ‘F’ if a is Fortran contiguous, ‘C’ otherwise. ‘K’ means match the layout of a as closely as possible. (Note that this function and numpy.copy are very similar but have different default values for their order= arguments, and this function always passes sub-classes through.) See also numpy.copy
Similar function with different default behavior numpy.copyto
Notes This function is the preferred method for creating an array copy. The function numpy.copy is similar, but it defaults to using order ‘K’, and will not pass sub-classes through by default. Examples >>> x = np.array([[1,2,3],[4,5,6]], order='F')
>>> y = x.copy()
>>> x.fill(0)
>>> x
array([[0, 0, 0],
[0, 0, 0]])
>>> y
array([[1, 2, 3],
[4, 5, 6]])
>>> y.flags['C_CONTIGUOUS']
True | numpy.reference.generated.numpy.recarray.copy |
numpy.recarray.ctypes attribute recarray.ctypes
An object to simplify the interaction of the array with the ctypes module. This attribute creates an object that makes it easier to use arrays when calling shared libraries with the ctypes module. The returned object has, among others, data, shape, and strides attributes (see Notes below) which themselves return ctypes objects that can be used as arguments to a shared library. Parameters
None
Returns
cPython object
Possessing attributes data, shape, strides, etc. See also numpy.ctypeslib
Notes Below are the public attributes of this object which were documented in “Guide to NumPy” (we have omitted undocumented public attributes, as well as documented private attributes): _ctypes.data
A pointer to the memory area of the array as a Python integer. This memory area may contain data that is not aligned, or not in correct byte-order. The memory area may not even be writeable. The array flags and data-type of this array should be respected when passing this attribute to arbitrary C-code to avoid trouble that can include Python crashing. User Beware! The value of this attribute is exactly the same as self._array_interface_['data'][0]. Note that unlike data_as, a reference will not be kept to the array: code like ctypes.c_void_p((a + b).ctypes.data) will result in a pointer to a deallocated array, and should be spelt (a + b).ctypes.data_as(ctypes.c_void_p)
_ctypes.shape
(c_intp*self.ndim): A ctypes array of length self.ndim where the basetype is the C-integer corresponding to dtype('p') on this platform (see c_intp). This base-type could be ctypes.c_int, ctypes.c_long, or ctypes.c_longlong depending on the platform. The ctypes array contains the shape of the underlying array.
_ctypes.strides
(c_intp*self.ndim): A ctypes array of length self.ndim where the basetype is the same as for the shape attribute. This ctypes array contains the strides information from the underlying array. This strides information is important for showing how many bytes must be jumped to get to the next element in the array.
_ctypes.data_as(obj)[source]
Return the data pointer cast to a particular c-types object. For example, calling self._as_parameter_ is equivalent to self.data_as(ctypes.c_void_p). Perhaps you want to use the data as a pointer to a ctypes array of floating-point data: self.data_as(ctypes.POINTER(ctypes.c_double)). The returned pointer will keep a reference to the array.
_ctypes.shape_as(obj)[source]
Return the shape tuple as an array of some other c-types type. For example: self.shape_as(ctypes.c_short).
_ctypes.strides_as(obj)[source]
Return the strides tuple as an array of some other c-types type. For example: self.strides_as(ctypes.c_longlong).
If the ctypes module is not available, then the ctypes attribute of array objects still returns something useful, but ctypes objects are not returned and errors may be raised instead. In particular, the object will still have the as_parameter attribute which will return an integer equal to the data attribute. Examples >>> import ctypes
>>> x = np.array([[0, 1], [2, 3]], dtype=np.int32)
>>> x
array([[0, 1],
[2, 3]], dtype=int32)
>>> x.ctypes.data
31962608 # may vary
>>> x.ctypes.data_as(ctypes.POINTER(ctypes.c_uint32))
<__main__.LP_c_uint object at 0x7ff2fc1fc200> # may vary
>>> x.ctypes.data_as(ctypes.POINTER(ctypes.c_uint32)).contents
c_uint(0)
>>> x.ctypes.data_as(ctypes.POINTER(ctypes.c_uint64)).contents
c_ulong(4294967296)
>>> x.ctypes.shape
<numpy.core._internal.c_long_Array_2 object at 0x7ff2fc1fce60> # may vary
>>> x.ctypes.strides
<numpy.core._internal.c_long_Array_2 object at 0x7ff2fc1ff320> # may vary | numpy.reference.generated.numpy.recarray.ctypes |
numpy.recarray.cumprod method recarray.cumprod(axis=None, dtype=None, out=None)
Return the cumulative product of the elements along the given axis. Refer to numpy.cumprod for full documentation. See also numpy.cumprod
equivalent function | numpy.reference.generated.numpy.recarray.cumprod |
numpy.recarray.cumsum method recarray.cumsum(axis=None, dtype=None, out=None)
Return the cumulative sum of the elements along the given axis. Refer to numpy.cumsum for full documentation. See also numpy.cumsum
equivalent function | numpy.reference.generated.numpy.recarray.cumsum |
numpy.recarray.data attribute recarray.data
Python buffer object pointing to the start of the array’s data. | numpy.reference.generated.numpy.recarray.data |
numpy.recarray.diagonal method recarray.diagonal(offset=0, axis1=0, axis2=1)
Return specified diagonals. In NumPy 1.9 the returned array is a read-only view instead of a copy as in previous NumPy versions. In a future version the read-only restriction will be removed. Refer to numpy.diagonal for full documentation. See also numpy.diagonal
equivalent function | numpy.reference.generated.numpy.recarray.diagonal |
numpy.recarray.dump method recarray.dump(file)
Dump a pickle of the array to the specified file. The array can be read back with pickle.load or numpy.load. Parameters
filestr or Path
A string naming the dump file. Changed in version 1.17.0: pathlib.Path objects are now accepted. | numpy.reference.generated.numpy.recarray.dump |
numpy.recarray.dumps method recarray.dumps()
Returns the pickle of the array as a string. pickle.loads will convert the string back to an array. Parameters
None | numpy.reference.generated.numpy.recarray.dumps |
numpy.recarray.fill method recarray.fill(value)
Fill the array with a scalar value. Parameters
valuescalar
All elements of a will be assigned this value. Examples >>> a = np.array([1, 2])
>>> a.fill(0)
>>> a
array([0, 0])
>>> a = np.empty(2)
>>> a.fill(1)
>>> a
array([1., 1.]) | numpy.reference.generated.numpy.recarray.fill |
numpy.recarray.flags attribute recarray.flags
Information about the memory layout of the array. Notes The flags object can be accessed dictionary-like (as in a.flags['WRITEABLE']), or by using lowercased attribute names (as in a.flags.writeable). Short flag names are only supported in dictionary access. Only the WRITEBACKIFCOPY, UPDATEIFCOPY, WRITEABLE, and ALIGNED flags can be changed by the user, via direct assignment to the attribute or dictionary entry, or by calling ndarray.setflags. The array flags cannot be set arbitrarily: UPDATEIFCOPY can only be set False. WRITEBACKIFCOPY can only be set False. ALIGNED can only be set True if the data is truly aligned. WRITEABLE can only be set True if the array owns its own memory or the ultimate owner of the memory exposes a writeable buffer interface or is a string. Arrays can be both C-style and Fortran-style contiguous simultaneously. This is clear for 1-dimensional arrays, but can also be true for higher dimensional arrays. Even for contiguous arrays a stride for a given dimension arr.strides[dim] may be arbitrary if arr.shape[dim] == 1 or the array has no elements. It does not generally hold that self.strides[-1] == self.itemsize for C-style contiguous arrays or self.strides[0] == self.itemsize for Fortran-style contiguous arrays is true. Attributes
C_CONTIGUOUS (C)
The data is in a single, C-style contiguous segment. F_CONTIGUOUS (F)
The data is in a single, Fortran-style contiguous segment. OWNDATA (O)
The array owns the memory it uses or borrows it from another object. WRITEABLE (W)
The data area can be written to. Setting this to False locks the data, making it read-only. A view (slice, etc.) inherits WRITEABLE from its base array at creation time, but a view of a writeable array may be subsequently locked while the base array remains writeable. (The opposite is not true, in that a view of a locked array may not be made writeable. However, currently, locking a base object does not lock any views that already reference it, so under that circumstance it is possible to alter the contents of a locked array via a previously created writeable view onto it.) Attempting to change a non-writeable array raises a RuntimeError exception. ALIGNED (A)
The data and all elements are aligned appropriately for the hardware. WRITEBACKIFCOPY (X)
This array is a copy of some other array. The C-API function PyArray_ResolveWritebackIfCopy must be called before deallocating to the base array will be updated with the contents of this array. UPDATEIFCOPY (U)
(Deprecated, use WRITEBACKIFCOPY) This array is a copy of some other array. When this array is deallocated, the base array will be updated with the contents of this array. FNC
F_CONTIGUOUS and not C_CONTIGUOUS. FORC
F_CONTIGUOUS or C_CONTIGUOUS (one-segment test). BEHAVED (B)
ALIGNED and WRITEABLE. CARRAY (CA)
BEHAVED and C_CONTIGUOUS. FARRAY (FA)
BEHAVED and F_CONTIGUOUS and not C_CONTIGUOUS. | numpy.reference.generated.numpy.recarray.flags |
numpy.recarray.flat attribute recarray.flat
A 1-D iterator over the array. This is a numpy.flatiter instance, which acts similarly to, but is not a subclass of, Python’s built-in iterator object. See also flatten
Return a copy of the array collapsed into one dimension. flatiter
Examples >>> x = np.arange(1, 7).reshape(2, 3)
>>> x
array([[1, 2, 3],
[4, 5, 6]])
>>> x.flat[3]
4
>>> x.T
array([[1, 4],
[2, 5],
[3, 6]])
>>> x.T.flat[3]
5
>>> type(x.flat)
<class 'numpy.flatiter'>
An assignment example: >>> x.flat = 3; x
array([[3, 3, 3],
[3, 3, 3]])
>>> x.flat[[1,4]] = 1; x
array([[3, 1, 3],
[3, 1, 3]]) | numpy.reference.generated.numpy.recarray.flat |
numpy.recarray.flatten method recarray.flatten(order='C')
Return a copy of the array collapsed into one dimension. Parameters
order{‘C’, ‘F’, ‘A’, ‘K’}, optional
‘C’ means to flatten in row-major (C-style) order. ‘F’ means to flatten in column-major (Fortran- style) order. ‘A’ means to flatten in column-major order if a is Fortran contiguous in memory, row-major order otherwise. ‘K’ means to flatten a in the order the elements occur in memory. The default is ‘C’. Returns
yndarray
A copy of the input array, flattened to one dimension. See also ravel
Return a flattened array. flat
A 1-D flat iterator over the array. Examples >>> a = np.array([[1,2], [3,4]])
>>> a.flatten()
array([1, 2, 3, 4])
>>> a.flatten('F')
array([1, 3, 2, 4]) | numpy.reference.generated.numpy.recarray.flatten |
numpy.recarray.getfield method recarray.getfield(dtype, offset=0)
Returns a field of the given array as a certain type. A field is a view of the array data with a given data-type. The values in the view are determined by the given type and the offset into the current array in bytes. The offset needs to be such that the view dtype fits in the array dtype; for example an array of dtype complex128 has 16-byte elements. If taking a view with a 32-bit integer (4 bytes), the offset needs to be between 0 and 12 bytes. Parameters
dtypestr or dtype
The data type of the view. The dtype size of the view can not be larger than that of the array itself.
offsetint
Number of bytes to skip before beginning the element view. Examples >>> x = np.diag([1.+1.j]*2)
>>> x[1, 1] = 2 + 4.j
>>> x
array([[1.+1.j, 0.+0.j],
[0.+0.j, 2.+4.j]])
>>> x.getfield(np.float64)
array([[1., 0.],
[0., 2.]])
By choosing an offset of 8 bytes we can select the complex part of the array for our view: >>> x.getfield(np.float64, offset=8)
array([[1., 0.],
[0., 4.]]) | numpy.reference.generated.numpy.recarray.getfield |
numpy.recarray.item method recarray.item(*args)
Copy an element of an array to a standard Python scalar and return it. Parameters
*argsArguments (variable number and type)
none: in this case, the method only works for arrays with one element (a.size == 1), which element is copied into a standard Python scalar object and returned. int_type: this argument is interpreted as a flat index into the array, specifying which element to copy and return. tuple of int_types: functions as does a single int_type argument, except that the argument is interpreted as an nd-index into the array. Returns
zStandard Python scalar object
A copy of the specified element of the array as a suitable Python scalar Notes When the data type of a is longdouble or clongdouble, item() returns a scalar array object because there is no available Python scalar that would not lose information. Void arrays return a buffer object for item(), unless fields are defined, in which case a tuple is returned. item is very similar to a[args], except, instead of an array scalar, a standard Python scalar is returned. This can be useful for speeding up access to elements of the array and doing arithmetic on elements of the array using Python’s optimized math. Examples >>> np.random.seed(123)
>>> x = np.random.randint(9, size=(3, 3))
>>> x
array([[2, 2, 6],
[1, 3, 6],
[1, 0, 1]])
>>> x.item(3)
1
>>> x.item(7)
0
>>> x.item((0, 1))
2
>>> x.item((2, 2))
1 | numpy.reference.generated.numpy.recarray.item |
numpy.recarray.itemset method recarray.itemset(*args)
Insert scalar into an array (scalar is cast to array’s dtype, if possible) There must be at least 1 argument, and define the last argument as item. Then, a.itemset(*args) is equivalent to but faster than a[args] = item. The item should be a scalar value and args must select a single item in the array a. Parameters
*argsArguments
If one argument: a scalar, only used in case a is of size 1. If two arguments: the last argument is the value to be set and must be a scalar, the first argument specifies a single array element location. It is either an int or a tuple. Notes Compared to indexing syntax, itemset provides some speed increase for placing a scalar into a particular location in an ndarray, if you must do this. However, generally this is discouraged: among other problems, it complicates the appearance of the code. Also, when using itemset (and item) inside a loop, be sure to assign the methods to a local variable to avoid the attribute look-up at each loop iteration. Examples >>> np.random.seed(123)
>>> x = np.random.randint(9, size=(3, 3))
>>> x
array([[2, 2, 6],
[1, 3, 6],
[1, 0, 1]])
>>> x.itemset(4, 0)
>>> x.itemset((2, 2), 9)
>>> x
array([[2, 2, 6],
[1, 0, 6],
[1, 0, 9]]) | numpy.reference.generated.numpy.recarray.itemset |
numpy.recarray.itemsize attribute recarray.itemsize
Length of one array element in bytes. Examples >>> x = np.array([1,2,3], dtype=np.float64)
>>> x.itemsize
8
>>> x = np.array([1,2,3], dtype=np.complex128)
>>> x.itemsize
16 | numpy.reference.generated.numpy.recarray.itemsize |
numpy.recarray.max method recarray.max(axis=None, out=None, keepdims=False, initial=<no value>, where=True)
Return the maximum along a given axis. Refer to numpy.amax for full documentation. See also numpy.amax
equivalent function | numpy.reference.generated.numpy.recarray.max |
numpy.recarray.mean method recarray.mean(axis=None, dtype=None, out=None, keepdims=False, *, where=True)
Returns the average of the array elements along given axis. Refer to numpy.mean for full documentation. See also numpy.mean
equivalent function | numpy.reference.generated.numpy.recarray.mean |
numpy.recarray.min method recarray.min(axis=None, out=None, keepdims=False, initial=<no value>, where=True)
Return the minimum along a given axis. Refer to numpy.amin for full documentation. See also numpy.amin
equivalent function | numpy.reference.generated.numpy.recarray.min |
numpy.recarray.nbytes attribute recarray.nbytes
Total bytes consumed by the elements of the array. Notes Does not include memory consumed by non-element attributes of the array object. Examples >>> x = np.zeros((3,5,2), dtype=np.complex128)
>>> x.nbytes
480
>>> np.prod(x.shape) * x.itemsize
480 | numpy.reference.generated.numpy.recarray.nbytes |
numpy.recarray.ndim attribute recarray.ndim
Number of array dimensions. Examples >>> x = np.array([1, 2, 3])
>>> x.ndim
1
>>> y = np.zeros((2, 3, 4))
>>> y.ndim
3 | numpy.reference.generated.numpy.recarray.ndim |
numpy.recarray.newbyteorder method recarray.newbyteorder(new_order='S', /)
Return the array with the same data viewed with a different byte order. Equivalent to: arr.view(arr.dtype.newbytorder(new_order))
Changes are also made in all fields and sub-arrays of the array data type. Parameters
new_orderstring, optional
Byte order to force; a value from the byte order specifications below. new_order codes can be any of: ‘S’ - swap dtype from current to opposite endian {‘<’, ‘little’} - little endian {‘>’, ‘big’} - big endian {‘=’, ‘native’} - native order, equivalent to sys.byteorder
{‘|’, ‘I’} - ignore (no change to byte order) The default value (‘S’) results in swapping the current byte order. Returns
new_arrarray
New array object with the dtype reflecting given change to the byte order. | numpy.reference.generated.numpy.recarray.newbyteorder |
numpy.recarray.nonzero method recarray.nonzero()
Return the indices of the elements that are non-zero. Refer to numpy.nonzero for full documentation. See also numpy.nonzero
equivalent function | numpy.reference.generated.numpy.recarray.nonzero |
numpy.recarray.partition method recarray.partition(kth, axis=- 1, kind='introselect', order=None)
Rearranges the elements in the array in such a way that the value of the element in kth position is in the position it would be in a sorted array. All elements smaller than the kth element are moved before this element and all equal or greater are moved behind it. The ordering of the elements in the two partitions is undefined. New in version 1.8.0. Parameters
kthint or sequence of ints
Element index to partition by. The kth element value will be in its final sorted position and all smaller elements will be moved before it and all equal or greater elements behind it. The order of all elements in the partitions is undefined. If provided with a sequence of kth it will partition all elements indexed by kth of them into their sorted position at once. Deprecated since version 1.22.0: Passing booleans as index is deprecated.
axisint, optional
Axis along which to sort. Default is -1, which means sort along the last axis.
kind{‘introselect’}, optional
Selection algorithm. Default is ‘introselect’.
orderstr or list of str, optional
When a is an array with fields defined, this argument specifies which fields to compare first, second, etc. A single field can be specified as a string, and not all fields need to be specified, but unspecified fields will still be used, in the order in which they come up in the dtype, to break ties. See also numpy.partition
Return a parititioned copy of an array. argpartition
Indirect partition. sort
Full sort. Notes See np.partition for notes on the different algorithms. Examples >>> a = np.array([3, 4, 2, 1])
>>> a.partition(3)
>>> a
array([2, 1, 3, 4])
>>> a.partition((1, 3))
>>> a
array([1, 2, 3, 4]) | numpy.reference.generated.numpy.recarray.partition |
numpy.recarray.prod method recarray.prod(axis=None, dtype=None, out=None, keepdims=False, initial=1, where=True)
Return the product of the array elements over the given axis Refer to numpy.prod for full documentation. See also numpy.prod
equivalent function | numpy.reference.generated.numpy.recarray.prod |
numpy.recarray.ptp method recarray.ptp(axis=None, out=None, keepdims=False)
Peak to peak (maximum - minimum) value along a given axis. Refer to numpy.ptp for full documentation. See also numpy.ptp
equivalent function | numpy.reference.generated.numpy.recarray.ptp |
numpy.recarray.put method recarray.put(indices, values, mode='raise')
Set a.flat[n] = values[n] for all n in indices. Refer to numpy.put for full documentation. See also numpy.put
equivalent function | numpy.reference.generated.numpy.recarray.put |
numpy.recarray.ravel method recarray.ravel([order])
Return a flattened array. Refer to numpy.ravel for full documentation. See also numpy.ravel
equivalent function ndarray.flat
a flat iterator on the array. | numpy.reference.generated.numpy.recarray.ravel |
numpy.recarray.repeat method recarray.repeat(repeats, axis=None)
Repeat elements of an array. Refer to numpy.repeat for full documentation. See also numpy.repeat
equivalent function | numpy.reference.generated.numpy.recarray.repeat |
numpy.recarray.reshape method recarray.reshape(shape, order='C')
Returns an array containing the same data with a new shape. Refer to numpy.reshape for full documentation. See also numpy.reshape
equivalent function Notes Unlike the free function numpy.reshape, this method on ndarray allows the elements of the shape parameter to be passed in as separate arguments. For example, a.reshape(10, 11) is equivalent to a.reshape((10, 11)). | numpy.reference.generated.numpy.recarray.reshape |
numpy.recarray.resize method recarray.resize(new_shape, refcheck=True)
Change shape and size of array in-place. Parameters
new_shapetuple of ints, or n ints
Shape of resized array.
refcheckbool, optional
If False, reference count will not be checked. Default is True. Returns
None
Raises
ValueError
If a does not own its own data or references or views to it exist, and the data memory must be changed. PyPy only: will always raise if the data memory must be changed, since there is no reliable way to determine if references or views to it exist. SystemError
If the order keyword argument is specified. This behaviour is a bug in NumPy. See also resize
Return a new array with the specified shape. Notes This reallocates space for the data area if necessary. Only contiguous arrays (data elements consecutive in memory) can be resized. The purpose of the reference count check is to make sure you do not use this array as a buffer for another Python object and then reallocate the memory. However, reference counts can increase in other ways so if you are sure that you have not shared the memory for this array with another Python object, then you may safely set refcheck to False. Examples Shrinking an array: array is flattened (in the order that the data are stored in memory), resized, and reshaped: >>> a = np.array([[0, 1], [2, 3]], order='C')
>>> a.resize((2, 1))
>>> a
array([[0],
[1]])
>>> a = np.array([[0, 1], [2, 3]], order='F')
>>> a.resize((2, 1))
>>> a
array([[0],
[2]])
Enlarging an array: as above, but missing entries are filled with zeros: >>> b = np.array([[0, 1], [2, 3]])
>>> b.resize(2, 3) # new_shape parameter doesn't have to be a tuple
>>> b
array([[0, 1, 2],
[3, 0, 0]])
Referencing an array prevents resizing… >>> c = a
>>> a.resize((1, 1))
Traceback (most recent call last):
...
ValueError: cannot resize an array that references or is referenced ...
Unless refcheck is False: >>> a.resize((1, 1), refcheck=False)
>>> a
array([[0]])
>>> c
array([[0]]) | numpy.reference.generated.numpy.recarray.resize |
numpy.recarray.round method recarray.round(decimals=0, out=None)
Return a with each element rounded to the given number of decimals. Refer to numpy.around for full documentation. See also numpy.around
equivalent function | numpy.reference.generated.numpy.recarray.round |
numpy.recarray.searchsorted method recarray.searchsorted(v, side='left', sorter=None)
Find indices where elements of v should be inserted in a to maintain order. For full documentation, see numpy.searchsorted See also numpy.searchsorted
equivalent function | numpy.reference.generated.numpy.recarray.searchsorted |
numpy.recarray.setfield method recarray.setfield(val, dtype, offset=0)
Put a value into a specified place in a field defined by a data-type. Place val into a’s field defined by dtype and beginning offset bytes into the field. Parameters
valobject
Value to be placed in field.
dtypedtype object
Data-type of the field in which to place val.
offsetint, optional
The number of bytes into the field at which to place val. Returns
None
See also getfield
Examples >>> x = np.eye(3)
>>> x.getfield(np.float64)
array([[1., 0., 0.],
[0., 1., 0.],
[0., 0., 1.]])
>>> x.setfield(3, np.int32)
>>> x.getfield(np.int32)
array([[3, 3, 3],
[3, 3, 3],
[3, 3, 3]], dtype=int32)
>>> x
array([[1.0e+000, 1.5e-323, 1.5e-323],
[1.5e-323, 1.0e+000, 1.5e-323],
[1.5e-323, 1.5e-323, 1.0e+000]])
>>> x.setfield(np.eye(3), np.int32)
>>> x
array([[1., 0., 0.],
[0., 1., 0.],
[0., 0., 1.]]) | numpy.reference.generated.numpy.recarray.setfield |
numpy.recarray.setflags method recarray.setflags(write=None, align=None, uic=None)
Set array flags WRITEABLE, ALIGNED, (WRITEBACKIFCOPY and UPDATEIFCOPY), respectively. These Boolean-valued flags affect how numpy interprets the memory area used by a (see Notes below). The ALIGNED flag can only be set to True if the data is actually aligned according to the type. The WRITEBACKIFCOPY and (deprecated) UPDATEIFCOPY flags can never be set to True. The flag WRITEABLE can only be set to True if the array owns its own memory, or the ultimate owner of the memory exposes a writeable buffer interface, or is a string. (The exception for string is made so that unpickling can be done without copying memory.) Parameters
writebool, optional
Describes whether or not a can be written to.
alignbool, optional
Describes whether or not a is aligned properly for its type.
uicbool, optional
Describes whether or not a is a copy of another “base” array. Notes Array flags provide information about how the memory area used for the array is to be interpreted. There are 7 Boolean flags in use, only four of which can be changed by the user: WRITEBACKIFCOPY, UPDATEIFCOPY, WRITEABLE, and ALIGNED. WRITEABLE (W) the data area can be written to; ALIGNED (A) the data and strides are aligned appropriately for the hardware (as determined by the compiler); UPDATEIFCOPY (U) (deprecated), replaced by WRITEBACKIFCOPY; WRITEBACKIFCOPY (X) this array is a copy of some other array (referenced by .base). When the C-API function PyArray_ResolveWritebackIfCopy is called, the base array will be updated with the contents of this array. All flags can be accessed using the single (upper case) letter as well as the full name. Examples >>> y = np.array([[3, 1, 7],
... [2, 0, 0],
... [8, 5, 9]])
>>> y
array([[3, 1, 7],
[2, 0, 0],
[8, 5, 9]])
>>> y.flags
C_CONTIGUOUS : True
F_CONTIGUOUS : False
OWNDATA : True
WRITEABLE : True
ALIGNED : True
WRITEBACKIFCOPY : False
UPDATEIFCOPY : False
>>> y.setflags(write=0, align=0)
>>> y.flags
C_CONTIGUOUS : True
F_CONTIGUOUS : False
OWNDATA : True
WRITEABLE : False
ALIGNED : False
WRITEBACKIFCOPY : False
UPDATEIFCOPY : False
>>> y.setflags(uic=1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: cannot set WRITEBACKIFCOPY flag to True | numpy.reference.generated.numpy.recarray.setflags |
numpy.recarray.size attribute recarray.size
Number of elements in the array. Equal to np.prod(a.shape), i.e., the product of the array’s dimensions. Notes a.size returns a standard arbitrary precision Python integer. This may not be the case with other methods of obtaining the same value (like the suggested np.prod(a.shape), which returns an instance of np.int_), and may be relevant if the value is used further in calculations that may overflow a fixed size integer type. Examples >>> x = np.zeros((3, 5, 2), dtype=np.complex128)
>>> x.size
30
>>> np.prod(x.shape)
30 | numpy.reference.generated.numpy.recarray.size |
numpy.recarray.sort method recarray.sort(axis=- 1, kind=None, order=None)
Sort an array in-place. Refer to numpy.sort for full documentation. Parameters
axisint, optional
Axis along which to sort. Default is -1, which means sort along the last axis.
kind{‘quicksort’, ‘mergesort’, ‘heapsort’, ‘stable’}, optional
Sorting algorithm. The default is ‘quicksort’. Note that both ‘stable’ and ‘mergesort’ use timsort under the covers and, in general, the actual implementation will vary with datatype. The ‘mergesort’ option is retained for backwards compatibility. Changed in version 1.15.0: The ‘stable’ option was added.
orderstr or list of str, optional
When a is an array with fields defined, this argument specifies which fields to compare first, second, etc. A single field can be specified as a string, and not all fields need be specified, but unspecified fields will still be used, in the order in which they come up in the dtype, to break ties. See also numpy.sort
Return a sorted copy of an array. numpy.argsort
Indirect sort. numpy.lexsort
Indirect stable sort on multiple keys. numpy.searchsorted
Find elements in sorted array. numpy.partition
Partial sort. Notes See numpy.sort for notes on the different sorting algorithms. Examples >>> a = np.array([[1,4], [3,1]])
>>> a.sort(axis=1)
>>> a
array([[1, 4],
[1, 3]])
>>> a.sort(axis=0)
>>> a
array([[1, 3],
[1, 4]])
Use the order keyword to specify a field to use when sorting a structured array: >>> a = np.array([('a', 2), ('c', 1)], dtype=[('x', 'S1'), ('y', int)])
>>> a.sort(order='y')
>>> a
array([(b'c', 1), (b'a', 2)],
dtype=[('x', 'S1'), ('y', '<i8')]) | numpy.reference.generated.numpy.recarray.sort |
numpy.recarray.squeeze method recarray.squeeze(axis=None)
Remove axes of length one from a. Refer to numpy.squeeze for full documentation. See also numpy.squeeze
equivalent function | numpy.reference.generated.numpy.recarray.squeeze |
numpy.recarray.std method recarray.std(axis=None, dtype=None, out=None, ddof=0, keepdims=False, *, where=True)
Returns the standard deviation of the array elements along given axis. Refer to numpy.std for full documentation. See also numpy.std
equivalent function | numpy.reference.generated.numpy.recarray.std |
numpy.recarray.strides attribute recarray.strides
Tuple of bytes to step in each dimension when traversing an array. The byte offset of element (i[0], i[1], ..., i[n]) in an array a is: offset = sum(np.array(i) * a.strides)
A more detailed explanation of strides can be found in the “ndarray.rst” file in the NumPy reference guide. See also numpy.lib.stride_tricks.as_strided
Notes Imagine an array of 32-bit integers (each 4 bytes): x = np.array([[0, 1, 2, 3, 4],
[5, 6, 7, 8, 9]], dtype=np.int32)
This array is stored in memory as 40 bytes, one after the other (known as a contiguous block of memory). The strides of an array tell us how many bytes we have to skip in memory to move to the next position along a certain axis. For example, we have to skip 4 bytes (1 value) to move to the next column, but 20 bytes (5 values) to get to the same position in the next row. As such, the strides for the array x will be (20, 4). Examples >>> y = np.reshape(np.arange(2*3*4), (2,3,4))
>>> y
array([[[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]],
[[12, 13, 14, 15],
[16, 17, 18, 19],
[20, 21, 22, 23]]])
>>> y.strides
(48, 16, 4)
>>> y[1,1,1]
17
>>> offset=sum(y.strides * np.array((1,1,1)))
>>> offset/y.itemsize
17
>>> x = np.reshape(np.arange(5*6*7*8), (5,6,7,8)).transpose(2,3,1,0)
>>> x.strides
(32, 4, 224, 1344)
>>> i = np.array([3,5,2,2])
>>> offset = sum(i * x.strides)
>>> x[3,5,2,2]
813
>>> offset / x.itemsize
813 | numpy.reference.generated.numpy.recarray.strides |
numpy.recarray.sum method recarray.sum(axis=None, dtype=None, out=None, keepdims=False, initial=0, where=True)
Return the sum of the array elements over the given axis. Refer to numpy.sum for full documentation. See also numpy.sum
equivalent function | numpy.reference.generated.numpy.recarray.sum |
numpy.recarray.swapaxes method recarray.swapaxes(axis1, axis2)
Return a view of the array with axis1 and axis2 interchanged. Refer to numpy.swapaxes for full documentation. See also numpy.swapaxes
equivalent function | numpy.reference.generated.numpy.recarray.swapaxes |
numpy.recarray.T attribute recarray.T
The transposed array. Same as self.transpose(). See also transpose
Examples >>> x = np.array([[1.,2.],[3.,4.]])
>>> x
array([[ 1., 2.],
[ 3., 4.]])
>>> x.T
array([[ 1., 3.],
[ 2., 4.]])
>>> x = np.array([1.,2.,3.,4.])
>>> x
array([ 1., 2., 3., 4.])
>>> x.T
array([ 1., 2., 3., 4.]) | numpy.reference.generated.numpy.recarray.t |
numpy.recarray.take method recarray.take(indices, axis=None, out=None, mode='raise')
Return an array formed from the elements of a at the given indices. Refer to numpy.take for full documentation. See also numpy.take
equivalent function | numpy.reference.generated.numpy.recarray.take |
numpy.recarray.tobytes method recarray.tobytes(order='C')
Construct Python bytes containing the raw data bytes in the array. Constructs Python bytes showing a copy of the raw contents of data memory. The bytes object is produced in C-order by default. This behavior is controlled by the order parameter. New in version 1.9.0. Parameters
order{‘C’, ‘F’, ‘A’}, optional
Controls the memory layout of the bytes object. ‘C’ means C-order, ‘F’ means F-order, ‘A’ (short for Any) means ‘F’ if a is Fortran contiguous, ‘C’ otherwise. Default is ‘C’. Returns
sbytes
Python bytes exhibiting a copy of a’s raw data. Examples >>> x = np.array([[0, 1], [2, 3]], dtype='<u2')
>>> x.tobytes()
b'\x00\x00\x01\x00\x02\x00\x03\x00'
>>> x.tobytes('C') == x.tobytes()
True
>>> x.tobytes('F')
b'\x00\x00\x02\x00\x01\x00\x03\x00' | numpy.reference.generated.numpy.recarray.tobytes |
numpy.recarray.tofile method recarray.tofile(fid, sep='', format='%s')
Write array to a file as text or binary (default). Data is always written in ‘C’ order, independent of the order of a. The data produced by this method can be recovered using the function fromfile(). Parameters
fidfile or str or Path
An open file object, or a string containing a filename. Changed in version 1.17.0: pathlib.Path objects are now accepted.
sepstr
Separator between array items for text output. If “” (empty), a binary file is written, equivalent to file.write(a.tobytes()).
formatstr
Format string for text file output. Each entry in the array is formatted to text by first converting it to the closest Python type, and then using “format” % item. Notes This is a convenience function for quick storage of array data. Information on endianness and precision is lost, so this method is not a good choice for files intended to archive data or transport data between machines with different endianness. Some of these problems can be overcome by outputting the data as text files, at the expense of speed and file size. When fid is a file object, array contents are directly written to the file, bypassing the file object’s write method. As a result, tofile cannot be used with files objects supporting compression (e.g., GzipFile) or file-like objects that do not support fileno() (e.g., BytesIO). | numpy.reference.generated.numpy.recarray.tofile |
numpy.recarray.tolist method recarray.tolist()
Return the array as an a.ndim-levels deep nested list of Python scalars. Return a copy of the array data as a (nested) Python list. Data items are converted to the nearest compatible builtin Python type, via the item function. If a.ndim is 0, then since the depth of the nested list is 0, it will not be a list at all, but a simple Python scalar. Parameters
none
Returns
yobject, or list of object, or list of list of object, or …
The possibly nested list of array elements. Notes The array may be recreated via a = np.array(a.tolist()), although this may sometimes lose precision. Examples For a 1D array, a.tolist() is almost the same as list(a), except that tolist changes numpy scalars to Python scalars: >>> a = np.uint32([1, 2])
>>> a_list = list(a)
>>> a_list
[1, 2]
>>> type(a_list[0])
<class 'numpy.uint32'>
>>> a_tolist = a.tolist()
>>> a_tolist
[1, 2]
>>> type(a_tolist[0])
<class 'int'>
Additionally, for a 2D array, tolist applies recursively: >>> a = np.array([[1, 2], [3, 4]])
>>> list(a)
[array([1, 2]), array([3, 4])]
>>> a.tolist()
[[1, 2], [3, 4]]
The base case for this recursion is a 0D array: >>> a = np.array(1)
>>> list(a)
Traceback (most recent call last):
...
TypeError: iteration over a 0-d array
>>> a.tolist()
1 | numpy.reference.generated.numpy.recarray.tolist |
numpy.recarray.tostring method recarray.tostring(order='C')
A compatibility alias for tobytes, with exactly the same behavior. Despite its name, it returns bytes not strs. Deprecated since version 1.19.0. | numpy.reference.generated.numpy.recarray.tostring |
numpy.recarray.trace method recarray.trace(offset=0, axis1=0, axis2=1, dtype=None, out=None)
Return the sum along diagonals of the array. Refer to numpy.trace for full documentation. See also numpy.trace
equivalent function | numpy.reference.generated.numpy.recarray.trace |
numpy.recarray.transpose method recarray.transpose(*axes)
Returns a view of the array with axes transposed. For a 1-D array this has no effect, as a transposed vector is simply the same vector. To convert a 1-D array into a 2D column vector, an additional dimension must be added. np.atleast2d(a).T achieves this, as does a[:, np.newaxis]. For a 2-D array, this is a standard matrix transpose. For an n-D array, if axes are given, their order indicates how the axes are permuted (see Examples). If axes are not provided and a.shape = (i[0], i[1], ... i[n-2], i[n-1]), then a.transpose().shape = (i[n-1], i[n-2], ... i[1], i[0]). Parameters
axesNone, tuple of ints, or n ints
None or no argument: reverses the order of the axes. tuple of ints: i in the j-th place in the tuple means a’s i-th axis becomes a.transpose()’s j-th axis.
n ints: same as an n-tuple of the same ints (this form is intended simply as a “convenience” alternative to the tuple form) Returns
outndarray
View of a, with axes suitably permuted. See also transpose
Equivalent function ndarray.T
Array property returning the array transposed. ndarray.reshape
Give a new shape to an array without changing its data. Examples >>> a = np.array([[1, 2], [3, 4]])
>>> a
array([[1, 2],
[3, 4]])
>>> a.transpose()
array([[1, 3],
[2, 4]])
>>> a.transpose((1, 0))
array([[1, 3],
[2, 4]])
>>> a.transpose(1, 0)
array([[1, 3],
[2, 4]]) | numpy.reference.generated.numpy.recarray.transpose |
numpy.recarray.var method recarray.var(axis=None, dtype=None, out=None, ddof=0, keepdims=False, *, where=True)
Returns the variance of the array elements, along given axis. Refer to numpy.var for full documentation. See also numpy.var
equivalent function | numpy.reference.generated.numpy.recarray.var |
numpy.recarray.view method recarray.view([dtype][, type])
New view of array with the same data. Note Passing None for dtype is different from omitting the parameter, since the former invokes dtype(None) which is an alias for dtype('float_'). Parameters
dtypedata-type or ndarray sub-class, optional
Data-type descriptor of the returned view, e.g., float32 or int16. Omitting it results in the view having the same data-type as a. This argument can also be specified as an ndarray sub-class, which then specifies the type of the returned object (this is equivalent to setting the type parameter).
typePython type, optional
Type of the returned view, e.g., ndarray or matrix. Again, omission of the parameter results in type preservation. Notes a.view() is used two different ways: a.view(some_dtype) or a.view(dtype=some_dtype) constructs a view of the array’s memory with a different data-type. This can cause a reinterpretation of the bytes of memory. a.view(ndarray_subclass) or a.view(type=ndarray_subclass) just returns an instance of ndarray_subclass that looks at the same array (same shape, dtype, etc.) This does not cause a reinterpretation of the memory. For a.view(some_dtype), if some_dtype has a different number of bytes per entry than the previous dtype (for example, converting a regular array to a structured array), then the behavior of the view cannot be predicted just from the superficial appearance of a (shown by print(a)). It also depends on exactly how a is stored in memory. Therefore if a is C-ordered versus fortran-ordered, versus defined as a slice or transpose, etc., the view may give different results. Examples >>> x = np.array([(1, 2)], dtype=[('a', np.int8), ('b', np.int8)])
Viewing array data using a different type and dtype: >>> y = x.view(dtype=np.int16, type=np.matrix)
>>> y
matrix([[513]], dtype=int16)
>>> print(type(y))
<class 'numpy.matrix'>
Creating a view on a structured array so it can be used in calculations >>> x = np.array([(1, 2),(3,4)], dtype=[('a', np.int8), ('b', np.int8)])
>>> xv = x.view(dtype=np.int8).reshape(-1,2)
>>> xv
array([[1, 2],
[3, 4]], dtype=int8)
>>> xv.mean(0)
array([2., 3.])
Making changes to the view changes the underlying array >>> xv[0,1] = 20
>>> x
array([(1, 20), (3, 4)], dtype=[('a', 'i1'), ('b', 'i1')])
Using a view to convert an array to a recarray: >>> z = x.view(np.recarray)
>>> z.a
array([1, 3], dtype=int8)
Views share data: >>> x[0] = (9, 10)
>>> z[0]
(9, 10)
Views that change the dtype size (bytes per entry) should normally be avoided on arrays defined by slices, transposes, fortran-ordering, etc.: >>> x = np.array([[1,2,3],[4,5,6]], dtype=np.int16)
>>> y = x[:, 0:2]
>>> y
array([[1, 2],
[4, 5]], dtype=int16)
>>> y.view(dtype=[('width', np.int16), ('length', np.int16)])
Traceback (most recent call last):
...
ValueError: To change to a dtype of a different size, the array must be C-contiguous
>>> z = y.copy()
>>> z.view(dtype=[('width', np.int16), ('length', np.int16)])
array([[(1, 2)],
[(4, 5)]], dtype=[('width', '<i2'), ('length', '<i2')]) | numpy.reference.generated.numpy.recarray.view |
numpy.record.all method record.all()
Scalar method identical to the corresponding array attribute. Please see ndarray.all. | numpy.reference.generated.numpy.record.all |
numpy.record.any method record.any()
Scalar method identical to the corresponding array attribute. Please see ndarray.any. | numpy.reference.generated.numpy.record.any |
numpy.record.argmax method record.argmax()
Scalar method identical to the corresponding array attribute. Please see ndarray.argmax. | numpy.reference.generated.numpy.record.argmax |
numpy.record.argmin method record.argmin()
Scalar method identical to the corresponding array attribute. Please see ndarray.argmin. | numpy.reference.generated.numpy.record.argmin |