Hi,
I don't understand what the meaning of the following lines returned by
model.matrix(). Can somebody help me understand it? What can they be
used for?
attr(,"assign")
[1] 0 1 2 2
attr(,"contrasts")
attr(,"contrasts")$A
[1] "contr.treatment"
attr(,"contrasts")$B
[1] "contr.treatment"
Regards,
Peng
> 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))
> afit=aov(Y ~ A + B,fr)
> model.matrix(afit)
(Intercept) A2 B2 B3
1 1 0 0 0
2 1 0 0 0
3 1 0 0 0
4 1 0 0 0
5 1 1 0 0
6 1 1 0 0
7 1 1 0 0
8 1 1 0 0
9 1 0 1 0
10 1 0 1 0
11 1 0 1 0
12 1 0 1 0
13 1 1 1 0
14 1 1 1 0
15 1 1 1 0
16 1 1 1 0
17 1 0 0 1
18 1 0 0 1
19 1 0 0 1
20 1 0 0 1
21 1 1 0 1
22 1 1 0 1
23 1 1 0 1
24 1 1 0 1
attr(,"assign")
[1] 0 1 2 2
attr(,"contrasts")
attr(,"contrasts")$A
[1] "contr.treatment"
attr(,"contrasts")$B
[1] "contr.treatment"
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