**From:** Sundar Dorai-Raj (*sundar.dorai-raj@pdf.com*)

**Date:** Thu 13 May 2004 - 02:44:03 EST

**Next message:**Liaw, Andy: "RE: [R] Design matrix not identity"**Previous message:**Jeff D. Hamann: "[R] summary table newbie question"**In reply to:**Patrik Waldmann: "[R] Design matrix not identity"**Next in thread:**Liaw, Andy: "RE: [R] Design matrix not identity"

Message-id: <40A25453.6050902@pdf.com>

Patrik Waldmann wrote:

*> Hello again,
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*>
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*> I was too quick before. What I was looking for was a function that
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*> constructs the design (or incidence) matrix (X in a linear model) from a
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*> factor. Uwe Ligges suggested using model.matrix and this does almost what I
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*> want, but it is first necessary to construct a data variable. It also asigns
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*> ones to all rows of the first column (because this is set to be the
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*> contrast, not really what I want - see below). Maybe time for a function
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*> that just converts a factor into a design matrix?
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*>
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*> I have a factor
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*> factor<-as.factor(c(1,1,2,2,3,3,3))
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*>
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*> and I want a matrix
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*> 1 0 0
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*> 1 0 0
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*> 0 1 0
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*> 0 1 0
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*> 0 0 1
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*> 0 0 1
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*> 0 0 1
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*>
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*>
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*> Patrik Waldmann###########################################
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model.matrix will do this for you.

R> fac <- as.factor(c(1, 1, 2, 2, 3, 3, 3))

R> model.matrix(~ fac - 1)

fac1 fac2 fac3

1 1 0 0

2 1 0 0

3 0 1 0

4 0 1 0

5 0 0 1

6 0 0 1

7 0 0 1

attr(,"assign")

[1] 1 1 1

attr(,"contrasts")

attr(,"contrasts")$fac

[1] "contr.treatment"

The "-1" drops the intercept.

Is this what you need?

--sundar

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**Next message:**Liaw, Andy: "RE: [R] Design matrix not identity"**Previous message:**Jeff D. Hamann: "[R] summary table newbie question"**In reply to:**Patrik Waldmann: "[R] Design matrix not identity"**Next in thread:**Liaw, Andy: "RE: [R] Design matrix not identity"

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