Your question seems rather poorly specified to me, and you may have to
clarify it further, but I'll make a stab at it.
IF one can assume that:
1. "a" must occur before "b", "b" before "c" etc. AND
2. "sec" is always increasing
THEN
z <- tapply(sec, ind, FUN = min)
gives the first appearance sec value for each letter and
outer(z,z,"-")
gives the matrix of differences (in which the upper triangle is the
negative of the lower)
Is that what you wanted?
-- Bert
On Wed, Nov 16, 2011 at 6:00 AM, Grant Gillis <grant.j.gil...@gmail.com> wrote:
> Dear List,
>
> I have data on a approximately 100 individuals visiting a a central logging
> station over a 1000 times. I would like to be able to calculate the
> distribution of inter-visit time intervals for all possible pairs am stuck
> on how to code for this. Single pairs are not a problem but extending it
> has been difficult for me. So for the toy data below I'd like to calculate
> for each 'a' how long until I see 'b' as well as for each 'b', how long
> until I see 'a' and so on for all possible pairs (2 triangle of a matrix?)
>
> Thanks for any help, hints, and suggestions.
>
> Grant
>
>
> toy data:
>
> ind <- c('a', 'b', 'a', 'c', 'b', 'b', 'c', 'a', 'c')
>
>
> sec <- c(1, 3, 5, 6, 12, 22, 66, 85, 99)
>
> What I am looking for
>
> ab
> 2
>
> [[alternative HTML version deleted]]
>
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>
--
Bert Gunter
Genentech Nonclinical Biostatistics
Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
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