Instant R Starter from Packpub.com is a book that I wish was available awhile ago. The book has information that I had to dig for when I needed it. Special values (NA, NaN, INF) NA is missing number. NaN not a number. And how they are used in R.
Clear directions on working with vectors. How vectors can be used as arguments of functions.
A clear concise book that is the missing piece. It covers R programming with code and examples of loops and how to make your own functions. The missing piece in my library of R books.