While going over the methods, I noticed they used #NMF where #PCA is mostly used. And while refreshing ;) my knowledge of the differences between the two, I stumbled upon a simple question/answer on #CrossValidated: https://stats.stackexchange.com/questions/502072/what-is-the-main-difference-between-pca-and-nmf-and-why-to-choose-one-rather-tha

This links to a book from #TrevorHastie, offered for free on his website: https://hastie.su.domains/publications.html

Another reason to finally have a look at "An Introduction to #Statistical Learning with Applications in R (second edition)" by James, Witten, et al.

#rstats