The only way that I can think of that would not use iteration would be to
create some type of lookup table with every possible vector you may ever
use, then lookup the results in that table.

If you are happy with internal iteration then one possibility is:

> x <- c(4,3,5)
> unlist(lapply(x,seq_len))
 [1] 1 2 3 4 1 2 3 1 2 3 4 5



On Fri, Dec 28, 2012 at 10:43 AM, Haoda Fu <fuhds@yahoo.com.cn> wrote:

> Hi,
>
> The data is
>
> x <- c(4,3,5);
> I need to translate it to
> y <- c(1,2,3,4,1,2,3,1,2,3,4,5);
> i.e. for each number in x, we need to generate 1:x and put it in y.
>
> The program need to evaluate this type of calculation for millions of
> times in simulation. Is there any elegant way to make this happen without
> iteration?
>
> Many thanks!!
>
> Best,
> Haoda
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>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280@gmail.com

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