Just Enough R
From the introduction: "R makes it easy to work with and learn from data. It also happens to be a complete programmming language, but if you’re reading this guide then that might not be of interest to you. That’s OK — the goal here is not to teach you how to program in R. The goal is to teach you just enough R to be confident to explore your data. In this guide, we use R in the same way we use any other statistics software: To check and visualise data, run statistical analyses, and share our results with others. To do that it’s worth learning the absolute basics of the R language and key recent extensions to it. "