On Wed, May 18, 2011 at 7:15 AM, Axel Urbiz <axel.ur...@gmail.com> wrote: > Dear experts: > > Is it possible to create a new function based > on stats:::model.matrix.default so that an alternative factor coding is used > when the function is called instead of the default factor coding? > > Basically, I'd like to reproduce the results in 'mat' below, without having > to explicitly specify my desired factor coding (identity matrices) in the > 'contrasts.arg'. > > dd <- data.frame(a = gl(3,4), b = gl(4,1,12)) > ca <- contrasts(dd$a, contrasts= FALSE) # 3 x 3 identity matrix > cb <- contrasts(dd$b, contrasts= FALSE) # 4 x 4 identity matrix > mat <- model.matrix(~ a + b, dd, contrasts.arg = list(a=ca, b=cb)) > > My approach was to modify the code in model.matrix by explicitly setting the > contrasts argument in the contr.identity and contrasts function to FALSE. > This is shown at the bottom of the email in the function model.matrix2: > > contr.identity <- contr.treatment > formals(contr.identity)$contrasts <- FALSE > > contrasts <- contrasts > formals(contrasts)$contrasts <- FALSE > > However, I believe this function is using contrasts = TRUE, as it doesn't > return the identity contrasts > mat2 <- model.matrix2(~ a + b, dd) > > Any help here is much appreciated. > Axel. >
If your objective in all this is ultimately to get lm coefficients in the original coding then see ?dummy.coef -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ 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.
