Using method dispatch to extend Lattice displays
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The lattice add-on package implements Trellis graphics for R using
low-level capabilities of the grid package.  One of the major recent
changes to the package API has been to make all high level functions
(xyplot, bwplot, cloud, etc.) generic functions, with the traditional
implementations available as the "formula" method.  This allows
cleaner and more flexible implementations for certain uses that were
permitted in the original S-PLUS version on a one-off basis.  For
example, dotplot() could be used to display one-way tables, but the
new approach naturally extends to multi-way tables as well.  More
importantly, it opens up the possibility for new Trellis displays
specifically designed for previously unsupported classes.  I will
discuss a few examples of such extensions (e.g. those now in the coda
package).  I will also describe issues relevant to the development of
new Trellis-style functions that make use of the framework provided by
lattice (e.g. hexbinplot and hexplom in the hexbin package).

Deepayan Sarkar
Computational Biology Program
Fred Hutchinson Cancer Research Center