[R] Splitting an array into two - alternate columns

[Ross Ihaka]

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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