Li, Bingshan wrote: > Hi Frank, > > I do not quite get you. What do you mean by simulation and speed issues? I do > not see why they have to be considered in logistic regression. > > Exactly. So don't use techniques that are only needed when such issues do have to be considered.
> Thanks. > > Bingshan > > ________________________________ > > From: Frank E Harrell Jr [mailto:[EMAIL PROTECTED] > Sent: Fri 6/29/2007 7:40 AM > To: Li, Bingshan > Cc: Seyed Reza Jafarzadeh; r-help@stat.math.ethz.ch > Subject: Re: [R] logistic regression and dummy variable coding > > > > 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 > > > > [[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.