[R] Matrix of dummy variables from a factor

[Doran, Harold]

Good point. Probably not for any subsequent use in R. But, I work in an
org that uses SAS, HLM, SPSS, among others. As a part of our control
processes at times we replicate analyses in different software programs.
For instance, we will replicate lmer functions using HLM. But, HLM
requires a matrix of dummy variables. So, I have used R to create this
matrix  for use in another software package that does need it.

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Berton Gunter
Sent: Tuesday, December 06, 2005 4:27 PM
To: 'Liaw, Andy'; 'Charles H. Franklin'; r-help at stat.math.ethz.ch
Subject: Re: [R] Matrix of dummy variables from a factor

But note: There are (almost?) no situations in R where the dummy
variables coding is needed. The coding is (almost?) always handled
properly by the modeling functions themselves.

Question: Can someone provide a "straightforward" example where the
dummy variable coding **is** explicitly needed?

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Liaw, Andy
> Sent: Tuesday, December 06, 2005 12:30 PM
> To: 'Charles H. Franklin'; r-help at stat.math.ethz.ch
> Subject: Re: [R] Matrix of dummy variables from a factor
> 
> See ?model.matrix.
> 
> HTH,
> Andy
> 
> From: Charles H. Franklin
> > 
> > What is a simple way to convert a factor into a matrix of dummy 
> > variables?
> > 
> > fm<-lm(y~f)
> > 
> > where f is a factor takes care of this in the estimation. 
> I'd like to
> > save the result of expanding f into a matrix for later use.
> > 
> > Thanks.
> > 
> > Charles
> > 
> > --
> > 
> > 
> >  Charles H. Franklin
> >  Professor, Political Science
> >  University of Wisconsin, Madison
> >  franklin at polisci.wisc.edu
> >  chfrankl at wisc.edu
> >  608-263-2022 (voice)
> >  608-265-2663 (fax)
> > 
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