[R] identify time span in date vector

[David Winsemius]

On Apr 3, 2012, at 9:35 AM, Fischer, Felix wrote:

> Hello everyone,
>
> i try to identify the first element of a date vector, for which the  
> following condition holds: at least 3 more dates within the next 365  
> days, but at least one of these must be between 3-12 month later.
>
> dates = as.Date(sort(rnorm(10,3000,100)), origin = "2000-1-1")
>
> Has anyone an idea how to do this economically? I'll need to apply  
> this to a large dataset with date vectors of various lengths and I  
> can think only of quite difficult algorithms :(
>

which( dates[4:(length(dates))] -dates[1:(length(dates)-3)] <365 &
        dates[3:(length(dates)-1)] -dates[1:(length(dates)-3)] > 90)

[1] 2 3

> Any ideas would be appreciated,
> Felix
>
>
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>
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David Winsemius, MD
West Hartford, CT