[R] changing model matrix restriction in lm()
gunter.berton at gene.com
Wed Oct 23 15:29:28 CEST 2013
On Wed, Oct 23, 2013 at 6:00 AM, Rafael Moral
<rafa_moral2004 at yahoo.com.br> 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
> 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,
> R-help at r-project.org mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Genentech Nonclinical Biostatistics
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