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Grolemund, Garrett, and Hadley Wickham. 2017. R for Data Science: Import, Tidy, Transform, Visualize, and Model Data. 1 edition. Houston: O’Reilly Media. http://r4ds.had.co.nz/.

Silge, Julia, and David Robinson. 2017. Text Mining with r: A Tidy Approach. 1 edition. O’Reilly Media. https://www.tidytextmining.com/.