[R] Counting indexes

[Alan Lue]

x <- rle(id)
cumsum(x$lengths) - (x$lengths - 1)
cumsum(x$lengths)

Alan


On Tue, May 25, 2010 at 10:00 PM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> 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
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Alan Lue
Master of Financial Engineering
UCLA Anderson School of Management