Dear Peng Yu, If this is indeed Peng Yu (as the email address seems to imply), I believe that you have a copy of my R and S-PLUS Companion to Applied Regression, where the answer is on p. 152, which describes the contrasts argument to lm; the contrasts argument to aov is similar. Hints: (1) the argument is named 'contrasts' and not 'contrasts.args' (as it is for model.matrix, the help page for which incidentally has a clear explanation with examples); (2) the argument takes a named list of contrasts for particular factors not a vector of contrasts with two elements.
John -------------------------------- John Fox Senator William McMaster Professor of Social Statistics Department of Sociology McMaster University Hamilton, Ontario, Canada web: socserv.mcmaster.ca/jfox > -----Original Message----- > From: pengyu...@gmail.com [mailto:pengyu...@gmail.com] On Behalf Of > bluesky...@gmail.com > Sent: February-09-10 11:44 PM > To: John Fox > Cc: r-h...@stat.math.ethz.ch > Subject: Re: [R] Model matrix using dummy regressors or deviation regressors > > On Tue, Feb 9, 2010 at 6:09 PM, John Fox <j...@mcmaster.ca> wrote: > > Dear bluesky315, > > > > There are several ways in R to determine regressors associated with > factors. > > One way is to set the global contrasts option. To get "deviation" > > regressors, use options(contrasts=c("contr.sum", "contr.poly")), and see > > ?options and ?contrasts for details. Also see Section 11.1.1 of the > > Introduction to R manual that comes with R. > > Instead of change the option globally, it is cleaner to pass the > contrast choice as an argument to aov(). It seems that 'contrasts.arg' > of model.matrix() can be used for this purpose. > > I tried something like contrasts.args=c('contr.sum', 'contr.poly'). > But it is not working. Would you please show me how to specify this > argument for the example that I gave in the original email? > > > I hope this helps, > > John > > > > -------------------------------- > > John Fox > > Senator William McMaster > > Professor of Social Statistics > > Department of Sociology > > McMaster University > > Hamilton, Ontario, Canada > > web: socserv.mcmaster.ca/jfox > > > > > >> -----Original Message----- > >> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > > On > >> Behalf Of bluesky...@gmail.com > >> Sent: February-09-10 6:33 PM > >> To: r-h...@stat.math.ethz.ch > >> Subject: [R] Model matrix using dummy regressors or deviation regressors > >> > >> The model matrix for the code at the end the email is shown below. > >> Since the model matrix doesn't have -1, I think that it is made of > >> dummy regressors rather than deviation regressors. I'm wondering how > >> to make a model matrix using deviation regressors. Could somebody let > >> me know? > >> > >> > model.matrix(aaov) > >> (Intercept) A2 B2 B3 A2:B2 A2:B3 > >> 1 1 0 0 0 0 0 > >> 2 1 0 0 0 0 0 > >> 3 1 0 0 0 0 0 > >> 4 1 0 0 0 0 0 > >> 5 1 1 0 0 0 0 > >> 6 1 1 0 0 0 0 > >> 7 1 1 0 0 0 0 > >> 8 1 1 0 0 0 0 > >> 9 1 0 1 0 0 0 > >> 10 1 0 1 0 0 0 > >> 11 1 0 1 0 0 0 > >> 12 1 0 1 0 0 0 > >> 13 1 1 1 0 1 0 > >> 14 1 1 1 0 1 0 > >> 15 1 1 1 0 1 0 > >> 16 1 1 1 0 1 0 > >> 17 1 0 0 1 0 0 > >> 18 1 0 0 1 0 0 > >> 19 1 0 0 1 0 0 > >> 20 1 0 0 1 0 0 > >> 21 1 1 0 1 0 1 > >> 22 1 1 0 1 0 1 > >> 23 1 1 0 1 0 1 > >> 24 1 1 0 1 0 1 > >> attr(,"assign") > >> [1] 0 1 2 2 3 3 > >> attr(,"contrasts") > >> attr(,"contrasts")$A > >> [1] "contr.treatment" > >> > >> attr(,"contrasts")$B > >> [1] "contr.treatment" > >> > >> > >> > >> ############# > >> a=2 > >> b=3 > >> n=4 > >> A = rep(sapply(1:a,function(x){rep(x,n)}),b) > >> B = as.vector(sapply(sapply(1:b, function(x){rep(x,n)}), > >> function(x){rep(x,a)})) > >> Y = A + B + rnorm(a*b*n) > >> > >> fr = data.frame(Y=Y,A=as.factor(A),B=as.factor(B)) > >> aaov=aov(Y ~ A * B,fr) > >> summary(aaov) > >> model.matrix(aaov) > >> > >> ______________________________________________ > >> 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. > > > > > > ______________________________________________ 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.
