> On Sat, 24 Jan 2004 [EMAIL PROTECTED] wrote: > > > I didn't get any response on this before, leading me to believe > > I've missed > > something fundamental. Can anybody guide me in the correct > > direction for more help on this?
Thanks for your reply: > You will need to explain to us why the object you list is `the design > matrix': have *you* a reference for that? R is doing the conventional > thing, and I at least have no idea where your example comes from. Perhaps I have used the wrong terminology? My understanding of a design matrix is that it identifies the factors are present for a given experiment. Here, I have a two factor experiment, where each factor has two levels. In the case I gave: t1 t2 1 1 0 2 1 1 3 0 0 4 0 1 I had expected this to represent four distinct experiments where factor one is present in the first two and absent in the second two. > You seem to have coded variables t1 and t2 the opposite ways (the > reference level is 2 for t1 and 1 for t2), and your model has the fit at > levels t1=2,t1=1 constrained to pass through the origin. I don't think R > has a simple syntax for that (although you can fake anything), and I find > it hard to believe that is actually what you want. That wasn't my intention, I want to retain the intercept term and not constrain it to pass through the origin. Paul > > > > Paul > > > > ================================================= > > I want to be able to create a design matrix with two factors. > For instance, if > > I have: > > > > > t1 <- factor(c(1,1,2,2)); > > > t2 <- factor(c(1,2,1,2)); > > > design <- model.matrix(~ -1 + (t1+t2)); > > > design; > > t11 t12 t22 > > 1 1 0 0 > > 2 1 0 1 > > 3 0 1 0 > > 4 0 1 1 > > > > But the design matrix I want is: > > t1 t2 > > 1 1 0 > > 2 1 1 > > 3 0 0 > > 4 0 1 > > > > Actually, in general I'm struggling with the syntax for > formulating a design > > matrix I can write down on paper. Is there a reference for > this beyond the R > > documentation? > > Chapter 6 of MASS has the most complete exposition (by Bill > Venables) that > I know of, and the White Book (Chambers & Hastie, 1992) goes well beyind > the R documentation (which uses it as the reference). > > -- > 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 > ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html