[R] Design matrix not identity

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From: Patrik Waldmann (Patrik.Waldmann@genfys.slu.se)
Date: Thu 13 May 2004 - 02:34:19 EST


Message-id: <9BE977B02923D311AADA00105AF497830365BFED@tilia.slu.se>

Hello again,

I was too quick before. What I was looking for was a function that
constructs the design (or incidence) matrix (X in a linear model) from a
factor. Uwe Ligges suggested using model.matrix and this does almost what I
want, but it is first necessary to construct a data variable. It also asigns
ones to all rows of the first column (because this is set to be the
contrast, not really what I want - see below). Maybe time for a function
that just converts a factor into a design matrix?

I have a factor
factor<-as.factor(c(1,1,2,2,3,3,3))

and I want a matrix
1 0 0
1 0 0
0 1 0
0 1 0
0 0 1
0 0 1
0 0 1

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