The documentation of xyplot could be improved here. It says: "If 'index.cond' is a list, it has to be as long as the number of conditioning variables, and the 'i'-th component has to be a valid indexing vector for the integer vector '1:nlevels(g_i)' (which can, among other things, repeat some of the levels or drop some altogether)."
It should make explicit that nlevels is the number of levels actually used in the data and not length(levels(f)). Cheers, Titus ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
