Deepayan will correct me if I'm wrong, but I'm pretty sure that the answer is that it looks in the frame in the data argument only for variables in the formula argument. Note that the fact that it also works for the subset argument is explicitly mentioned therein:
subset: logical or integer indexing vector **(can be specified in terms of variables in data). ** FWIW, I agree that this is not as clearly documented as I think it could be: I kind of intuited it after a bunch of trial and error. Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Jacob Wegelin Sent: Monday, October 12, 2009 9:33 AM To: r-h...@stat.math.ethz.ch Subject: [R] xyplot does not find variable in data When we call a lattice function such as xyplot, to what extent does the "data" designation cause the function to look inside the "data" for variables? In the examples below, the "subset" argument understands that "Variety" is a variable in the data. But the "scales" argument does not understand that "nitro" is a variable in the data. What principle is at work? library(MEMSS) # The following works fine: xyplot( yield ~ nitro , data=Oats , scales=list( x=list( at=unique(Oats$nitro) ) ) , subset=Variety=="Victory" ) # But the following returns an error: xyplot( yield ~ nitro , data=Oats , scales=list( x=list( at=unique(nitro) ) ) ) Thanks for any insight Jacob A. Wegelin Assistant Professor Department of Biostatistics Virginia Commonwealth University 730 East Broad Street Room 3006 P. O. Box 980032 Richmond VA 23298-0032 U.S.A. E-mail: jwege...@vcu.edu URL: http://www.people.vcu.edu/~jwegelin ______________________________________________ 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. ______________________________________________ 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.