Complete financial econemtrics university course with best intro to R including math principles
http://www.math.uncc.edu/~zcai/FE-notes.pdf
An R intro from the same professor with math principles (one of the best I have seen)
http://www.math.uncc.edu/~zcai/r-notes.pdf
If you are new to R and wanting to learn quant, I would start with the link above