Interacting with Trellis Displays

High-level functions in lattice produce “trellis” objects that can be thought of as abstract representations of visualizations. An actual rendering of a visualization is produced by plotting the corresponding object using the appropriate print() or plot() method. In this chapter, we discuss things the user can do after this plotting has been completed.

One possible approach is to treat the result as any other graphic created using the grid package, and make further enhancements to the display using the low-level tools available in grid. In particular, the display consists of a tree of viewports, and various grid graphical objects (grobs) drawn within them. The user can move down to any of these viewports and add further objects, or, less commonly, edit the properties of existing objects. The precise details of these operations are beyond the scope of this book, but are discussed by Murrell (2005). In this chapter, we focus entirely on a higher-level interface in the lattice package for similar tasks, which is less flexible,1 but usually sufficient. The playwith package (Andrews, 2007) provides a user-friendly GUI wrapper for many of these facilities.