R help - Jan 2009 - remove columns containing all zeros (or other value)

Hello-

I would like to remove the columns of a matrix that contain all zeros. 
For example, from
 x<-matrix(c(1,5,3,2,1,4,0,0,0), ncol=3,nrow=3)

I would like to remove the third column. However, because this is in a 
loop I need a way to first determine which columns are all zeros, and 
only then remove them. I.e., I don't know which column of x contains all 
zeros until after x is created.

Thanks!

Anthony

-- 
Anthony Steven Dick, Ph.D.
Post-Doctoral Fellow
Human Neuroscience Laboratory
Department of Neurology
The University of Chicago
5841 S. Maryland Ave. MC-2030
Chicago, IL 60637
Phone: (773)-834-7770
Email: adick at uchicago.edu
Web: http://home.uchicago.edu/~adick/

Hi Anthony,
Try this:

 x[,apply(x,2,function(x) !all(x==0))]


HTH,

Jorge


On Wed, Jan 14, 2009 at 5:01 PM, Anthony Dick <adick@uchicago.edu> wrote:
> Hello-
>
> I would like to remove the columns of a matrix that contain all zeros. For
> example, from
> x<-matrix(c(1,5,3,2,1,4,0,0,0), ncol=3,nrow=3)
>
> I would like to remove the third column. However, because this is in a loop
> I need a way to first determine which columns are all zeros, and only then
> remove them. I.e., I don't know which column of x contains all zeros
until
> after x is created.
>
> Thanks!
>
> Anthony
>
> --
> Anthony Steven Dick, Ph.D.
> Post-Doctoral Fellow
> Human Neuroscience Laboratory
> Department of Neurology
> The University of Chicago
> 5841 S. Maryland Ave. MC-2030
> Chicago, IL 60637
> Phone: (773)-834-7770
> Email: adick@uchicago.edu
> Web: http://home.uchicago.edu/~adick/
>
> ______________________________________________
> R-help@r-project.org mailing list
> 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.
>
	[[alternative HTML version deleted]]

You can also try this:

x[,-(which(colSums(x) == 0))]

Cheers,

Gustavo.

On Wed, Jan 14, 2009 at 8:01 PM, Anthony Dick <adick at uchicago.edu>
wrote:
> Hello-
>
> I would like to remove the columns of a matrix that contain all zeros. For
> example, from
> x<-matrix(c(1,5,3,2,1,4,0,0,0), ncol=3,nrow=3)
>
> I would like to remove the third column. However, because this is in a loop
> I need a way to first determine which columns are all zeros, and only then
> remove them. I.e., I don't know which column of x contains all zeros
until
> after x is created.
>
> Thanks!
>
> Anthony
>
> --
> Anthony Steven Dick, Ph.D.
> Post-Doctoral Fellow
> Human Neuroscience Laboratory
> Department of Neurology
> The University of Chicago
> 5841 S. Maryland Ave. MC-2030
> Chicago, IL 60637
> Phone: (773)-834-7770
> Email: adick at uchicago.edu
> Web: http://home.uchicago.edu/~adick/
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>

How about:

remove.constant.values<-function(x,MARGIN,value2remove) {
 is.constant.line<-function(x,value2remove) { return(any(x!=value2remove)) }
 return(unlist(apply(x,MARGIN,is.constant.line,value2remove)))
}

x[,remove.constant.values(x,2,0)]

Jim