I would argue this is a bug in model.frame(), but it seems that it is S-compatible. That is, variables excluded by - appear in the model frame even though they do not really appear in the simplified formula. (I suppose the rationale is that - need not always interpreted as deletion.)
The proposed fix regretably will not work, since one can do things like library(MASS) prcomp(~ dist + dist:climb, hills) I'll see if I can dream up a general solution. (One way forward is to simplify the formula and call terms again, but simplifcation is rather clumsy code.) On Sat, 25 Mar 2006, Berwin A Turlach wrote: > Dear all, > > perhaps I am using princomp.formula and prcomp.formula in a way that > is not documented to work, but then the documentation just says: > > formula: a formula with no response variable. > > Thus, to avoid a lot of typing, it would be nice if one could use '.' > and '-' in the formula, e.g. > >> library(DAAG) >> res <- prcomp(~ . - case - site - Pop - sex, possum) > Error in prcomp.formula(~. - case - site - Pop - sex, possum) : > PCA applies only to numerical variables >> res <- princomp(~ . - case - site - Pop - sex, possum) > Error in princomp.formula(~. - case - site - Pop - sex, possum) : > PCA applies only to numerical variables > > Unfortunately, as the examples above show, this is currently not > possible, since both functions test whether any term mentioned in the > formula is non numeric or a factor, instead of just testing those that > enter the analysis. > > The attached patch should allow the use of '.' and '-', while still > producing an error when a factor or a non-numeric variable is > specified to enter the analysis: > >> library(DAAG) >> res <- prcomp(~ . - case - site - Pop - sex, possum) >> res <- princomp(~ . - case - site - Pop - sex, possum) >> res <- prcomp(~ . - case - site - Pop, possum) > Error in prcomp.formula(~. - case - site - Pop, possum) : > PCA applies only to numerical variables >> res <- princomp(~ . - case - site - Pop, possum) > Error in princomp.formula(~. - case - site - Pop, possum) : > PCA applies only to numerical variables > > On my machine, `make check FORCE=FORCE' succeeds with this patch and, > as far as I can tell, no modification of the help pages would be > necessary. > > Cheers, > > Berwin > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
