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/