In this final section, we consider advanced topics that will enhance your skills as an R programmer. Chapter 19 completes our discussion of graphics with detailed information on how to customize graphs created with the ggplot2 package. You’ll learn to modify a graph’s titles, labels, axes, colors, fonts, legends, and more. You’ll also learn to combine several graphs into one overall image and turn a static graph into an interactive web graphic.
Chapter 20 reviews the R language at a deeper level. This includes a discussion of R’s object-oriented programming features, working with environments, and advanced function writing. Tips for writing efficient code and debugging programs are also given. Although chapter 20 is more technical than the other chapters in this book, it provides extensive practical advice for developing more useful programs.