useful python packages
ntlk: https://www.youtube.com/watch?v=FLZvOKSCkxY&list=PLQVvvaa0QuDf2JswnfiGkliBInZnIC4HL&index=1
gensim: https://github.com/RaRe-Technologies/gensim/blob/develop/tutorials.md#tutorials
sklearn: http://www.developintelligence.com/blog/2017/03/predicting-yelp-star-ratings-review-text-python/
useful R packages
tm: https://cran.r-project.org/web/packages/tm/vignettes/tm.pdf
idea from kaggle: https://www.kaggle.com/c/yelp-recruiting/discussion/4980
text classification using neural network http://www.developintelligence.com/blog/2017/06/practical-neural-networks-keras-classifying-yelp-reviews/