Hi All, Now it works. Thanks for all your answers and the explanations are very clear.
Bingshan 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]] >> >> ______________________________________________ >> [email protected] 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. >> ______________________________________________ [email protected] 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.
