[R] Intersection of two sets of intervals

[Thomas Meyer]

Stavros, you are quite correct -- I discovered that the hard way a 
little while ago when testing my two-line solution. Use of pmin/pmax 
don't handle, for instance, cases where more than one interval in one 
set is wholly contained by an interval in the other. (I have a 
mis-posted msg awaiting moderator approval in R-help with a concrete 
example.)

Your tip to check out the intervals pkg looks promising. FYI, there the 
general intersection is computed as the complement of the union of the 
complements, i.e. A*B = (A'+B')' , aka DeMorgan.

Thanks for the help,

-tom

On 4/15/2009 11:27 AM, Stavros Macrakis wrote:
> I can see how pmax/pmin would easily allow the intersection of
> corresponding elements of two sequences of intervals, but I don't see
> how they help in intersecting two *sets* of intervals, which was the
> original problem statement.
> 
>             -s
> 
> 
> 
> On Wed, Apr 15, 2009 at 9:14 AM, ONKELINX, Thierry
> <Thierry.ONKELINX at inbo.be> wrote:
>> Not of the self but still not complicated:
>>
>> list1 <- data.frame(open=c(1,5), close=c(2,10))
>> list2 <- data.frame(open=c(1.5,3), close=c(2.5,10))
>>
>> Intersec <- data.frame(Open = pmax(list1$open, list2$open), Close =
>> pmin(list1$close, list2$close))
>> Intersec[Intersec$Open > Intersec$Close, ] <- NA
>> Intersec
>>
>> HTH,
>>
>> Thierry
>>
>> ------------------------------------------------------------------------
>> ----
>> ir. Thierry Onkelinx
>> Instituut voor natuur- en bosonderzoek / Research Institute for Nature
>> and Forest
>> Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
>> methodology and quality assurance
>> Gaverstraat 4
>> 9500 Geraardsbergen
>> Belgium
>> tel. + 32 54/436 185
>> Thierry.Onkelinx at inbo.be
>> www.inbo.be
>>
>> To call in the statistician after the experiment is done may be no more
>> than asking him to perform a post-mortem examination: he may be able to
>> say what the experiment died of.
>> ~ Sir Ronald Aylmer Fisher
>>
>> The plural of anecdote is not data.
>> ~ Roger Brinner
>>
>> The combination of some data and an aching desire for an answer does not
>> ensure that a reasonable answer can be extracted from a given body of
>> data.
>> ~ John Tukey
>>
>> -----Oorspronkelijk bericht-----
>> Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
>> Namens Thomas Meyer
>> Verzonden: woensdag 15 april 2009 14:59
>> Aan: r-help at r-project.org
>> Onderwerp: [R] Intersection of two sets of intervals
>>
>> Hi,
>>
>> Algorithm question: I have two sets of "intervals", where an interval is
>>
>> an ordered pair [a,b] of two numbers. Is there an efficient way in R to
>> generate the intersection of two lists of same?
>>
>> For concreteness: I'm representing a set of intervals with a data.frame:
>>
>>  > list1 = as.data.frame(list(open=c(1,5), close=c(2,10)))
>>  > list1
>>   open close
>> 1    1     2
>> 2    5    10
>>
>>  > list2 = as.data.frame(list(open=c(1.5,3), close=c(2.5,10)))
>>  > list2
>>   open close
>> 1  1.5   2.5
>> 2  3.0  10.0
>>
>> How do I get the intersection which would be something like:
>>   open close
>> 1  1.5   2.0
>> 2  5.0  10.0
>>
>> I wonder if there's some ready-built functionality that might help me
>> out. I'm new to R and am still learning to vectorize my code and my
>> thinking. Or maybe there's a package for interval arithmetic that I can
>> just pull off the shelf.
>>
>> Thanks,
>>
>> -tom
>>
>> --
>> Thomas Meyer
>>
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