about model.matrix
This is a big topic. You might try looking for tutorials on "linear models", with "rank" or "rank deficiency" as subtopics. One possible book is: http://www.amazon.com/Linear-Models-Chapman-Statistical-Science/dp/1439887330/ref=sr_1_5?s=books&ie=UTF8&qid=1427987551&sr=1-5&keywords=linear+models+in+statistics ... but there are dozens. Better yet, consult a local statistical expert for help. Trying to educate yourself is laudable, but may be unrealistic. Cheers, Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." Clifford Stoll
On Thu, Apr 2, 2015 at 7:20 AM, Fix Ace <acefix at rocketmail.com> wrote:
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
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-- Michael http://www.dewey.myzen.co.uk/home.html [[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.