R statistic
http://pluto.huji.ac.il/~msby/StatThink/index.html
CRAN has a growing list of contributed documentation in a variety of languages.
https://cran.r-project.org/other-docs.html
R igraph
https://rstudio-pubs-static.s3.amazonaws.com/74248_3bd99f966ed94a91b36d39d8f21e3dc3.html
R data structure
https://www.stat.berkeley.edu/~nolan/stat133/Fall05/lectures/RIntro4.pdf