[R] Switching entries in vector in by groups of two

From: David Afshartous <dafshartous_at_med.miami.edu>
Date: Fri, 27 Jun 2008 10:11:26 -0400

All,

I have a long vector that contains an even number of entries. I'd like to switch the 1st and 2nd entry, the 3rd and 4th, and so on, without writing a loop.

This code works:

X = c(8, 10, 6, 3, 20, 1)
index = c(2,1,4,3,6,5)
X[index]

But for a long list is there a way to generate the index? I can get the parts to the index as:

index.odd = seq(1,length(X), by = 2)
index.even = index.odd + 1

Is there a simple way to interweave them to produce the desired index? Or is there a better way?

Cheers,
David



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