[R] How do I obtain the design matrix of an lm()?

Bert Gunter gunter.berton at gene.com
Wed Oct 10 17:31:56 CEST 2007

If all you're doing is fitting different responses to the same X data, then
you don't need model.matrix. See ?update, ?update.formula. 

Bert Gunter
Genentech Nonclinical Statistic

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Ajay Shah
Sent: Tuesday, October 09, 2007 7:34 AM
To: R-help
Subject: [R] How do I obtain the design matrix of an lm()?

I am using the clever formula notation of R to first do an OLS. E.g. I

  m <- lm(y ~ x + f)

where f is a factor, and R automatically constructs the dummy
variables. Very nice.

I need to then go on to do some other ML estimation using the same
design matrix that's used for the OLS. I could, of course, do this
manually. But it seems that lm() has done all this hard work. I wonder
if there's a way to ask him nicely so as to get it. :-)

Ajay Shah                                      http://www.mayin.org/ajayshah

ajayshah at mayin.org
<*(:-? - wizard who doesn't know the answer.

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