about model.matrix
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
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