tokens: Just so this may help someone trying to convert a factor variable with levels 0 and 1 into labels for input to XGBoost , you need to be aware that you need to subtract 1 after converting to integer ( or numeric ) :
ner_tags: O O O O O O O O O O O O O O B-Value O B-Value O O O O O B-Library O O O O O O O O O O O B-Value O O O B-Data_Type O O B-Data_Type O O