[R] How to subset a matrix?

[Petr Savicky]

On Tue, Jun 12, 2012 at 11:44:51AM -0500, Michael wrote:
> Hi all,
> 
> Lets say I have a matrix A which is m x n.
> 
> I also have a mask matrix MASK which is m x n with values in T/F, where T
> values make a sub-matrix in regutangular shape...
> 
> I applied B=A[MASK] and it didn't work as expected...

Hi.

Try the following.

  A <- matrix(1:16, nrow=4, ncol=4)
  B <- matrix(FALSE, nrow=4, ncol=4)
  B[2:3, 2:3] <- TRUE
  A[rowSums(B) != 0, colSums(B) != 0]

       [,1] [,2]
  [1,]    6   10
  [2,]    7   11

Hope this helps.

Petr Savicky.