I haven't seen a better introduction to R than Paul Teetor's R Cookbook, published by O'Reilly. While it follows the familiar O'Reilly cookbook format, it also provides a gentle introduction, with all the necessary information to get started As a particularly nice touch for a cookbook, it includes basic statistics and input/output in the early chapters so that the reader doesn't need to wade through (or fearfully skip over) a lot of material before getting to the needed resources.
A common complaint with other R resources is that the novice in
statistics is overwhelmed with statistical terminology. Teetor
is not trying to provide a statistics textbook, but he includes refreshing
explanations for the underlying statistics.
Some chapters are particular standouts:
Chapter 2: Some Basics. This chapter is an appetizer of what R can do,
and it's very helpful to get this early. Aside from the basic usage of R covered in this chapter, section 2.6 (Computing Basic Statistics) provides a quick introduction to performing basic statistics with R.
Chapter 4: Input and Output. R's input/output support is a bit cumbersome, but the R Cookbook provides examples for many common cases that newcomers need to handle (text files, CSV's, etc).
Chapter 9: General Statistics. This is the meat and potatoes of R for many statistical users. Students in a basic statistics course (or practitioners needing to do most fundamental analyses) will find chapter 9 to be indispensable.
Chapter 10: Graphics provides a nice dessert as visualizing data is often critical to understanding it. Teetor provides simple, concrete examples that cover many of the common graphics, as well as how to handle their titles, labels, and legends.
As an added bonus, Teetor and O'Reilly provide Chapter 14: Time Series Analysis. The coverage here goes beyond standard cookbook fare and provides a good starting point for those interested in Time Series Analysis.
Overall, the R Cookbook is the best O'Reilly cookbook I've read since the release of the Perl Cookbook, and it's by far the best introduction to R that I've seen. It's a must-have for every newcomer to R.
[Disclaimer: I got this book for free as part of the Oreilly blogger review program I was not required to write a positive review. The opinions I have expressed are my own. I am disclosing this in accordance with the Federal Trade Commission’s 16 CFR, Part 255 : “Guides Concerning the Use of Endorsements and Testimonials in Advertising.”]