R is an Open Source implementation of the S language.
The main mode of presentation is via code examples with liberal commenting of the code an.
This book provides an elementary-level introduction to R, targeting both non-statistician scientists in various fields and students of statistics.
R is now in widespread use for teaching at many levels as well as for practical data analysis and methodological development.
It works on multiple computing platforms and can be freely downloaded.
R is an Open Source implementation of the S language