remove columns containing all zeros (or other value)

Careful:

x <- matrix(c(1, 5, 3, 2, 1, 4, -1, 0, 1),
? ? ? ? ? ? ncol = 3, nrow = 3)

x

? ? ?[,1] [,2] [,3]
[1,] ? ?1 ? ?2 ? -1
[2,] ? ?5 ? ?1 ? ?0
[3,] ? ?3 ? ?4 ? ?1

x[, colSums(x) != 0]

? ? ?[,1] [,2]
[1,] ? ?1 ? ?2
[2,] ? ?5 ? ?1
[3,] ? ?3 ? ?4

Not quite the result wanted... ?:-)

Try this:

x[, colSums(x == 0) != nrow(x)]

? ? ?[,1] [,2]
[1,] ? ?1 ? ?2
[2,] ? ?5 ? ?1
[3,] ? ?3 ? ?4

x <- matrix(c(1, 5, 3, 2, 1, 4, -1, 0, 1),
? ? ? ? ? ? ? ncol = 3, nrow = 3)

x[, colSums(x == 0) != nrow(x)]

? ? ?[,1] [,2] [,3]
[1,] ? ?1 ? ?2 ? -1
[2,] ? ?5 ? ?1 ? ?0
[3,] ? ?3 ? ?4 ? ?1

HTH,

Marc Schwartz

on 01/14/2009 04:29 PM Gustavo Carvalho wrote:

Sorry for the double post, but this is probably faster:

x[, colSums(x) != 0]

On Wed, Jan 14, 2009 at 8:22 PM, Gustavo Carvalho
<gustavo.bi... at gmail.com> wrote:

You can also try this:

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

Cheers,

Gustavo.

On Wed, Jan 14, 2009 at 8:01 PM, Anthony Dick <ad... 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