tokens: I 've tried using a sql query with sqldf , but subqueries can only return 1 value at a time , which would mean running the query all over for every new column I want to define ( and I want to add many more derivative columns later ) .
ner_tags: O O O O O B-Language O O B-Library O O O O O O O O O O O O O O O O O O O O O O O B-Data_Structure O O O O O O O O O O O O O B-Data_Structure O O O