Chapter 19 Reference
Dotson, Marc. “Introduction to Text Analysis in R”. DataCamp. https://www.datacamp.com/courses/introduction-to-text-analysis-in-r.,
String Manipulation in R with stringr, Text Mining: Bag of Words, Sentiment Analysis in R.
Other DataCamp Courses Sentiment Analysis in R: The Tidy Way, Topic Modeling in R, Introduction to Natural Language Processing in R.
There are also some projects in DataCamp, and tutorial.