[R] Remove columns

[Steve Lianoglou]

Hi Alberto,

On Aug 18, 2009, at 4:14 AM, Alberto Lora M wrote:

> Hi Everbody
>
> Could somebody help me.?
>
> I need to remove the columns where the sum of it components is equal  
> to
> zero.
>
> For example
>
>> a<-matrix(c(0,0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,1,1,0,0,1,0), ncol=4)
>> a
>     [,1] [,2] [,3] [,4]
> [1,]    0    0    0    1
> [2,]    0    1    0    1
> [3,]    0    0    0    0
> [4,]    0    1    0    0
> [5,]    0    0    0    1
> [6,]    0    0    0    0
>
> Columns 1 and 3 should be removed
>
> the result should be the dollowing matrix
>
>     [,2]  [,4]
> [1,]    0    1
> [2,]    1    1
> [3,]    0    0
> [4,]    1    0
> [5,]    0    1
> [6,]    0    0

Try this:

R> a[,-which(colSums(a) == 0)]
      [,1] [,2]
[1,]    0    1
[2,]    1    1
[3,]    0    0
[4,]    1    0
[5,]    0    1
[6,]    0    0

Indexing into a matrix/vector/data.frame/list/whatever with a negative  
number removes those elements from the result.

-steve

--
Steve Lianoglou
Graduate Student: Computational Systems Biology
   |  Memorial Sloan-Kettering Cancer Center
   |  Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact