Advanced Panel Functions

R is a complete programming language that allows, and indeed encourages, its users to go beyond the canned uses built into the system. The transition from user to programmer can be intimidating for the beginner to contemplate, but is almost inevitable after a point. In the context of lattice, this transition is most often necessitated by a desire to customize the display in small ways, perhaps just to add a common reference line to all panels. Such customizations are fairly basic in any serious use of lattice, and we have seen a number of examples throughout this book. In this chapter, which is meant for the more advanced user, we take a more formal look at panel functions, give pointers to the tools that might help in writing new ones, and finally discuss some nontrivial examples.