On Tue, Dec 1, 2009 at 4:04 PM, Charles C. Berry <cbe...@tajo.ucsd.edu> wrote: > On Tue, 1 Dec 2009, Peng Yu wrote: > >> Could somebody recommend some textbook how to compute contrast when >> there are interactions terms? "Applied Linear Regression Models" >> (book) mentioned contrast, but I cannot extend it to the case where >> there are interaction terms. > > > Textbook? Schmextbook! > > You have the power of R at your fingertips! > > Use it to explore concepts you are trying to wrap your brain around! > > >> df <- expand.grid(x1=1:20,x2=factor(letters[1:2])) >> vanilla <- model.matrix(~0+poly(x1,degree=3), df ) >> matplot(row( vanilla) , vanilla, type='b') >> inter <- model.matrix(~0+poly(x1,degree=3):x2, df ) >> matplot(row( inter ) , inter, type='b')
I don't understand. Where the contrast is? BTW, what does 'schmextbook' mean? ______________________________________________ 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.
