Here are some references I’ve found particularly useful when developing or debugging R code. When trying something new, I like to have a user’s guide open at my left elbow, a language reference guide open at my right elbow, and a steaming cup above the keyboard. (With R, that cup usually needs to be a soothing glass of Riesling instead of the usual jolt of coffee.) When debugging, I like to have a debugger reference on the left, and a large unloaded revolver at my right. (The bugs find the revolver intimidating, and I find that angry clicking sound more rewarding than admitting my programming errors.)
To effectively learn a new programming language, I like having a well-organized written framework that guides my perspective on the structure and use of that language. Here are a couple of on-line documents that provide that kind of framework.
R User’s Guides
These focus on techniques for using specific methods. They are generally stronger than beginner’s introductions.
R Reference Guides
These provide encyclopedic reference on the details of function and syntax.
R Style Guides
These provide some best practices on structuring the code.
The better organized on-line tutorials easily serve as user’s guides.
(R logo provided courtesy of R Foundation, distributed under Creative Commons Attribution-ShareAlike 4.0 International license.)