Hi. Here are two approaches:

c(mapply(function(x,y) rep(c(x,y), 2), (1:10)[c(T,F)], (1:10)[c(F,T)]))

c(tapply(1:10, rep(1:(10/2), each=2), rep, 2), recursive=T)

Andrija





On Mon, Nov 11, 2013 at 1:11 PM, Federico Calboli
<f.calboli@imperial.ac.uk>wrote:

> Hi All,
>
> I am trying to create an index that returns something like
>
> 1,2,1,2,3,4,3,4,5,6,5,6,7,8,7,8
>
> and so on and so forth until a predetermined value (which is obviously
> even).  I am trying very hard to avoid for loops or for loops front ends.
>
> I'd be obliged if anybody could offer a suggestion.
>
> BW
>
> F
>
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