[R] calculating time interval distributions

Bert Gunter gunter.berton at gene.com
Wed Nov 16 16:20:09 CET 2011

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


z <- tapply(sec, ind, FUN = min)

gives the first appearance sec value for each letter and


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.gillis at 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

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