Hi:

Here's another approach:

library(reshape)
l <- list(a1, a2, a3, a4)
ll <- melt(l)
ll[ll$value %in% i, 'L1']
# [1] 1 3

HTH,
Dennis

On Thu, Jun 17, 2010 at 4:40 PM, song song <rprojecthelp@gmail.com> wrote:

> for example, I have
>
> a1=c(1,3,5)
> a2=c(2,4,6)
> a3=c(7,8)
> a4=c(9,10)
>
> now if I have i=5, so i in a1, then I get a feedback tag[5]=1
>                   i=8,  so i in a3, then can get tag[8]=3
>
> in there any function to do this to check the element belongs to which
> group?
>
> thank you!!!
>
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