[R] Counting indexes

[Gabor Grothendieck]

This assumes that for a particular id they all occur together in a run:

> cbind(start = which(!duplicated(id)), end = which(!duplicated(id, fromLast = TRUE)))
     start end
[1,]     1   1
[2,]     2   3
[3,]     4   6
[4,]     7   7
[5,]     8   9


On Wed, May 26, 2010 at 12:14 AM, Robin Jeffries <rjeffries at ucla.edu> wrote:
> Hallo!
>
> I have a vector of ID's like so,
> id <- c(1,2,2,3,3,3,4,5,5)
>
> I would like to create a [start,stop] pair of vectors that index the first
> and last observation per ID.
>
> For the ID list above, it would look like
> 1 1
> 2 3
> 4 6
> 7 7
> 8 9
>
> I haven't worked with indexes/data manipulation much in R, so any pointers
> would be helpful.
>
> Many thanks!
>
> ~~~~~~~~~~~~~~~~~~~
> -Robin Jeffries
> Dr.P.H. Candidate in Biostatistics
> UCLA School of Public Health
> rjeffries at ucla.edu
> 530-624-0428
>
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