Bingshan Li wrote: > Hi All, > > Now it works. Thanks for all your answers and the explanations are > very clear. > > Bingshan
But note that you are not using R correctly unless you are doing a simulation and have some special speed issues. Let the model functions do all this for you. Frank > > On Jun 28, 2007, at 7:44 PM, Seyed Reza Jafarzadeh wrote: > >> NewVar <- relevel( factor(OldVar), ref = "b") >> should create a dummy variable, and change the reference category >> for the model. >> >> Reza >> >> >> On 6/28/07, Bingshan Li <[EMAIL PROTECTED]> wrote: >>> Hello everyone, >>> >>> I have a variable with several categories and I want to convert this >>> into dummy variables and do logistic regression on it. I used >>> model.matrix to create dummy variables but it always picked the >>> smallest one as the reference. For example, >>> >>> model.matrix(~.,data=as.data.frame(letters[1:5])) >>> >>> will code 'a' as '0 0 0 0'. But I want to code another category as >>> reference, say 'b'. How to do it in R using model.matrix? Is there >>> other way to do it if model.matrix has no such functionality? >>> >>> Thanks! >>> >>> >>> >>> [[alternative HTML version deleted]] >>> >>> ______________________________________________ >>> R-help@stat.math.ethz.ch 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@stat.math.ethz.ch 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. > -- Frank E Harrell Jr Professor and Chair School of Medicine Department of Biostatistics Vanderbilt University ______________________________________________ R-help@stat.math.ethz.ch 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.