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

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Fri, 27 Jun 2008 10:14:01 -0400

You can do it without and index like this:

c(matrix(X, 2)[2:1,])

or if you need the index for some purpose apart from this:

c(matrix(seq_along(X), 2)[2:1,])

On Fri, Jun 27, 2008 at 10:11 AM, David Afshartous <dafshartous_at_med.miami.edu> wrote:
>
> 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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>



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 27 Jun 2008 - 14:17:52 GMT

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