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

[Ben Fairbank]

Perhaps 

xnew <- x[1:length(x)+c(1,-1)]

will do it.

Ben Fairbank 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of David Afshartous
Sent: Friday, June 27, 2008 9:11 AM
To: r-help at r-project.org
Subject: [PS] [R] Switching entries in vector in by groups of two


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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