Message-ID: <590951224.3724632.1427984454648.JavaMail.yahoo@mail.yahoo.com>
Date: 2015-04-02T14:20:54Z
From: Fix Ace
Subject: about model.matrix
In-Reply-To: <551C15AE.8050208@dewey.myzen.co.uk>
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
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