[R] about model.matrix

[Michael Dewey]

You cannot have columns which are linearly dependent.

Starting a project which uses statistics without having some sort of 
local statistical backup seems unprofitable.

install.packages("fortunes") # if not already done
library(fortunes)
fortune(122)

On 02/04/2015 15:20, Fix Ace 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
>
>  >
>  >     [[alternative HTML version deleted]]
>  >
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>
> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>
>
>

-- 
Michael
http://www.dewey.myzen.co.uk/home.html