[R] assign sequence numbers by group of value

[Gabor Grothendieck]

This was recently discussed in:
 http://tolstoy.newcastle.edu.au/R/help/06/06/28664.html
Note that it depends on the groups elements being contiguous:

seq(id) - match(id, id) + 1

On 6/10/06, Tony Chu <gatony at gmail.com> wrote:
>  Dear R users:
>
>  I would like to assign sequence numbers based on group of value but
> cannot find an easy way.
> Here is a simple instance:
>
> > id = c('a','a','a','b','c','c')
> > id
> [1] "a" "a" "a" "b" "c" "c"
>
> I hope to create a corresponding vector as --
>
> [1]  1   2   3   1   1   2
>
> That is, in group "a"  the number begins with 1 and then continues to plus 1
> until
> it happens to the next group.  For "b" It goes back to 1.  Because there is
> only one
> b, it begins to be 1 again for the first c following, etc.  Could someone
> advise me
> how to do this in programming rather than manually?  Thanks a lot.
>
>  Tony C.
>
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>
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