Learn R

Cost

Start with An Introduction to R. The pdf version is more readable than the html version, likely because the authors of R are from the academic world and are rendering html as an afterthought (i.e. with LaTeX).

See CRAN: Contributed Documentation for R for Beginners by Emmanuel Paradis (PDF), as suggested in the preface to SR2.

Functional programming resources:

• Select a function from the apply family

• Call apply-like function on each row of a dataframe

To debug, you can insert browser in the code, or run options(error = browser) (see ref) to open the debugger on errors. See also debug, in particular debugonce.