[R] changing model matrix restriction in lm()

[Greg Snow]

Also look at ?relevel

On Wed, Oct 23, 2013 at 7:45 AM, Rafael Moral
<rafa_moral2004 at yahoo.com.br> wrote:
> 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
>  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.
>
>
>
>  --
>
>  Bert Gunter
>  Genentech Nonclinical Biostatistics
>
>  (650) 467-7374
>
> ______________________________________________
> R-help at r-project.org 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.



-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com