# [R] Model matrix using dummy regressors or deviation regressors

David Winsemius dwinsemius at comcast.net
Wed Feb 10 00:47:11 CET 2010

```On Feb 9, 2010, at 6:33 PM, bluesky315 at gmail.com wrote:

> The model matrix for the code at the end the email is shown below.
> Since the model matrix doesn't have -1, I think that it is made of
> dummy regressors rather than deviation regressors. I'm wondering how
> to make a model matrix using deviation regressors. Could somebody let
> me know?

If I understand your terminology, then:

?contr.sum

--
David.
>
>> model.matrix(aaov)
>   (Intercept) A2 B2 B3 A2:B2 A2:B3
> 1            1  0  0  0     0     0
> 2            1  0  0  0     0     0
> 3            1  0  0  0     0     0
> 4            1  0  0  0     0     0
> 5            1  1  0  0     0     0
> 6            1  1  0  0     0     0
> 7            1  1  0  0     0     0
> 8            1  1  0  0     0     0
> 9            1  0  1  0     0     0
> 10           1  0  1  0     0     0
> 11           1  0  1  0     0     0
> 12           1  0  1  0     0     0
> 13           1  1  1  0     1     0
> 14           1  1  1  0     1     0
> 15           1  1  1  0     1     0
> 16           1  1  1  0     1     0
> 17           1  0  0  1     0     0
> 18           1  0  0  1     0     0
> 19           1  0  0  1     0     0
> 20           1  0  0  1     0     0
> 21           1  1  0  1     0     1
> 22           1  1  0  1     0     1
> 23           1  1  0  1     0     1
> 24           1  1  0  1     0     1
> attr(,"assign")
> [1] 0 1 2 2 3 3
> attr(,"contrasts")
> attr(,"contrasts")\$A
> [1] "contr.treatment"
>
> attr(,"contrasts")\$B
> [1] "contr.treatment"
>
>
>
> #############
> a=2
> b=3
> n=4
> A = rep(sapply(1:a,function(x){rep(x,n)}),b)
> B = as.vector(sapply(sapply(1:b, function(x){rep(x,n)}), function(x)
> {rep(x,a)}))
> Y = A + B + rnorm(a*b*n)
>
> fr = data.frame(Y=Y,A=as.factor(A),B=as.factor(B))
> aaov=aov(Y ~ A * B,fr)
> summary(aaov)
> model.matrix(aaov)
>
> ______________________________________________
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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.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

```

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