Text for individual panels in a trellis plot

["John Payne" <jcpayne@u.washington.edu>]

Hi all.  I am creating trellis plots of the form xyplot(y ~ x | factorA *
factorB, groups = observed), where observed is a 2-level factor ("observed"
or "expected").  The problem is that I want to label some, but not all, of
the panels with the text "No data" (some panels are blank because they
didn't have enough data to fit a curve, while others are blank because that
combination of factorA and factorB is missing from the experiment.  I want
to label the latter).  Can anyone suggest a straightforward solution?  I
have struggled fruitlessly to figure out the scope of variables within the
nested and not-so-transparent panel functions.

Thanks!

John Payne
Department of Zoology
University of Washington
Seattle, WA 98195