?duplicated will help.
M
On Dec 27, 2012, at 8:17 PM, Emmanuel Levy <emmanuel.l...@gmail.com> wrote:
> Hi,
>
> That sounds simple but I cannot think of a really fast way of getting
> the following:
>
> c(1,1,2,2,3,3,4,4) would give c(1,3,5,7)
>
> i.e., a function that returns the indexes of the first occurrences of numbers.
>
> Note that numbers may have any order e.g., c(3,4,1,2,1,1,2,3,5), can
> be very large, and the vectors are also very large (which prohibits
> any loop).
>
> The best I could think of is:
>
> tmp = c(1,1,2,2,3,3,4,4)
> u = unique(tmp)
> sapply(u, function(x){ which(!is.na(match(tmp,x)))[1]} )
>
> But there might be a useful function I don't know ..
>
> Thanks for any hint.
> All the best,
>
> Emmanuel
>
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