about model.matrix
Thank you very much for the response. Then what does it mean? I am not a stat person, but have to use it for my project. :( Could you please recommend some readings about it? Thanks a lot!
On Wednesday, April 1, 2015 10:58 AM, Michael Dewey <lists at dewey.myzen.co.uk> wrote:
This is really a question about statistics rather than R but see below
On 01/04/2015 06:28, Fix Ace wrote:
I tried to run the sample code from R:
dd <- data.frame(a = gl(3,4), b = gl(4,1,12))? a b
1? 1 1
2? 1 2
3? 1 3
4? 1 4
5? 2 1
6? 2 2
7? 2 3
8? 2 4
9? 3 1
10 3 2
11 3 3
12 3 4
options("contrasts")
model.matrix(~ a + b, dd)(Intercept) a2 a3 b2 b3 b4
1? ? ? ? ? ? 1? 0? 0? 0? 0? 0
2? ? ? ? ? ? 1? 0? 0? 1? 0? 0
3? ? ? ? ? ? 1? 0? 0? 0? 1? 0
4? ? ? ? ? ? 1? 0? 0? 0? 0? 1
5? ? ? ? ? ? 1? 1? 0? 0? 0? 0
6? ? ? ? ? ? 1? 1? 0? 1? 0? 0
7? ? ? ? ? ? 1? 1? 0? 0? 1? 0
8? ? ? ? ? ? 1? 1? 0? 0? 0? 1
9? ? ? ? ? ? 1? 0? 1? 0? 0? 0
10? ? ? ? ? 1? 0? 1? 1? 0? 0
11? ? ? ? ? 1? 0? 1? 0? 1? 0
12? ? ? ? ? 1? 0? 1? 0? 0? 1
when I tried to remove the intercept from the matrix, I used the following codemodel.matrix(~ 0+a + b, dd)
? a1 a2 a3 b2 b3 b41 1 0 0 0 0 02 1 0 0 1 0 03 1 0 0 0 1 04 1 0 0 0 0 15 0 1 0 0 0 06 0 1 0 1 0 07 0 1 0 0 1 08 0 1 0? 0 0 19 0 0 1 0 0 010 0 0 1 1 0 011 0 0 1 0 1 012 0 0 1 0 0 1 when I tried to remove the intercept
That got mangled but In your matrix below try forming the sum of a1+a2+a3 and the sum of b1+b2+b3+b4. I think you will find they are linearly related.
Here I noticed that, all levels of a, a1, a2, and a3, were included. I wonder how? I can include the "b1" in the matrix as well?? a1 a2 a3 b1 b2 b3 b4 1? 1? 0? 0? 1? 0? 0? 0 2? 1? 0? 0? 0? 1? 0? 0 3? 1? 0? 0? 0? 0? 1? 0 4? 1? 0? 0? 0? 0? 0? 1 5? 0? 1? 0? 1? 0? 0? 0 6? 0? 1? 0? 0? 1? 0? 0 7? 0? 1? 0? 0? 0? 1? 0 8? 0? 1? 0? 0? 0? 0? 1 9? 0? 0? 1? 1? 0? 0? 0 10? 0? 0? 1? 0? 1? 0? 0 11? 0? 0? 1? 0? 0? 1? 0 12? 0? 0? 1? 0? 0? 0? 1 ??? [[alternative HTML version deleted]]
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Michael http://www.dewey.myzen.co.uk/home.html [[alternative HTML version deleted]]