If you’re ever fumbling around with data in R, you’re probably familiar with the built-in, unattractive graphics. ggplot2’s been increasingly recognized as a necessity for getting the most out of your imagery. It offers nearly complete control over your graphics output, building them layer by layer.
I spent a solid year learning and exploring R as a graduate student before I cracked open Winston Chang’s R Graphics Cookbook and started learning ggplot2’s little oddities. ggplot2 is itself almost like another language within R, but it’s thankfully a very simple language — far more simple and far more flexible, I feel, than the built-in graphics options.