[R] changing model matrix restriction in lm()

[Rafael Moral]

Thank you very much!

Best,
Rafael.

--------------------------------------------
Em qua, 23/10/13, Bert Gunter <gunter.berton at gene.com> escreveu:

 Assunto: Re: [R] changing model matrix restriction in lm()

 Cc: "r-help at r-project.org" <r-help at r-project.org>
 Data: Quarta-feira, 23 de Outubro de 2013, 11:29

 ?contrasts
 ?C

 Cheers,
 Bert

 On Wed, Oct 23, 2013 at 6:00 AM, Rafael Moral

 wrote:
 > Dear useRs,
 > I was wondering if there was a way of changing the
 model matrix restriction automatically in the formula
 statement when fitting a model using, for example, lm().
 > When we do
 >
 > set.seed(100)
 > y <- rnorm(12)
 > A <- gl(3, 4)
 > summary(lm(y ~ A))
 >
 > we obtain A1=0 as a baseline and A2 and A3 as effects.
 > However, if I want to use A2=0 as a baseline, I can do
 >
 > X <- cbind(1, model.matrix(lm(y ~ A - 1)))[,-3]
 > summary(lm(y ~ X))
 >
 > I wonder if there is a way of specifying the
 restriction in the parameters directly in the formula
 argument instead of building the desired model matrix.
 >
 > Best wishes,
 > Rafael.
 >
 > ______________________________________________
 > R-help at r-project.org
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 > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
 > and provide commented, minimal, self-contained,
 reproducible code.



 -- 

 Bert Gunter
 Genentech Nonclinical Biostatistics

 (650) 467-7374