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.