# [R] Splitting an array into two - alternate columns

Ross Ihaka ihaka at stat.auckland.ac.nz
Thu Nov 23 21:39:50 CET 2000

```On Fri, Nov 24, 2000 at 12:46:37AM +0000, Phil Rhoades wrote:
> I want to split an array (A1) into two arrays using alternate columns eg
>
> A2 would consist of:
>
> A1[,1], A1[,3], A1[,5], . .
>
> A3 would consist of:
>
> A1[,2], A1[,4], A1[,6], . .
>
> Anyone got a nice method?

I'm a big fan of brute force and ignorance!

asplit <-
function(X)
list(odd = x[,seq(1, ncol(x), by = 2)],
even = x[,seq(2, ncol(x), by = 2)])

> x <- matrix(1:10,nr=2)
> x
[,1] [,2] [,3] [,4] [,5]
[1,]    1    3    5    7    9
[2,]    2    4    6    8   10
> asplit(x)
\$odd
[,1] [,2] [,3]
[1,]    1    5    9
[2,]    2    6   10

\$even
[,1] [,2]
[1,]    3    7
[2,]    4    8

Ross
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```