Welcome to a Little Book of R for Bioinformatics! by Avril Coghlan.
From the webpage:
This is a simple introduction to bioinformatics, with a focus on genome analysis, using the R statistics software.
To encourage research into neglected tropical diseases such as leprosy, Chagas disease, trachoma, schistosomiasis etc., most of the examples in this booklet are for analysis of the genomes of the organisms that cause these diseases.
A Little Book of R For Bioinformatics, Release 01 (PDF)
Seventy-seven pages, including answers to exercises that should get you going with R in bioinformatics.