[R] Matrix manipulation

Julian Burgos
Mon, 22 Oct 2007 22:29:20 -0000

Matrices are not made of paper! :)  If you index a matrix with negative
numbers, you'll get back that matrix minus that column or row.

A quick example:

 >a<-matrix(c(1:9),ncol=3)  # Create a sample matrix
 >a 			   # Display it
      [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

 >a[,2] # Get the second column
[1] 4 5 6

 >a[,-2] # Everything except the second column

      [,1] [,2]
[1,]    1    7
[2,]    2    8
[3,]    3    9

Julian



yiferic at berkeley.edu wrote:
> Hi everyone,
>
> suppose I have a 2D matrix, is there a command to snip out a specific
> row/column and then remerge the remaining columns/rows back into a
> contiguous matrix? I will need to repeat this operation quite a
> bit(reverse selection).
>
> Thanks for any insights you can offer.
>
> Yifei
>
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