The R installation needs to be done at OS level. Just go to http://cran.r-project.org/ and download R.
Then install the "R Project" Splunk App (https://apps.splunk.com/app/1735/) and specify the path to the R binary in app's Setup screen.
As far as I know there is no RPM package for R.
great title, but the article is a bit short.
Please explicit what "R" is.