On Wed, Apr 21, 2010 at 4:26 PM, Peter Dalgaard <pda...@gmail.com> wrote: > As for case #1, the rules are tricky in cases where interactions are > present without main effects, but AFAICS, what you observe is > essentially the same effect as > >> model.matrix(~fac-1, contrasts=list(fac="contr.sum")) > fac1 fac2 fac3 > 1 1 0 0 > 2 1 0 0 > 3 1 0 0 > 4 1 0 0 > 5 1 0 0 > 6 0 1 0 > 7 0 1 0 > 8 0 1 0 > 9 0 1 0 > 10 0 1 0 > 11 0 0 1 > 12 0 0 1 > 13 0 0 1 > 14 0 0 1 > 15 0 0 1 > attr(,"assign") > [1] 1 1 1 > attr(,"contrasts") > attr(,"contrasts")$fac > [1] "contr.sum" > > > I.e., that R reverts to using indicator variables when the intercept is > absent.
Is there any nice way of getting contr.sum coding for the interaction as opposed to the ugly code in my post that I used to force it? i.e. cbind(1, model.matrix(~ fac)[,2:3] * scores) ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel