RMarkdown tutorial:
https://github.com/ccs-amsterdam/r-course-material/blob/master/tutorials/r_text_lda.md
Video series about topic modeling:
https://www.youtube.com/watch?v=ELct2RRENQM&list=PLjXODJ_lGN_WtxhPsQ_t0aHtFAcsIh1-8
More tutorial stuff:
https://github.com/ccs-amsterdam/r-course-material
Good article on preprocessing for unsupervised ml:
https://pdfs.semanticscholar.org/95e0/c468a19afc6173053234c7fe660033363ffb.pdf