Re: [Boost-users] [ICL] interval_map question

Subject: Re: [Boost-users] [ICL] interval_map question
From: Joachim Faulhaber (afojgo_at_[hidden])
Date: 2011-05-26 05:31:58

Another side note on this to make the issue more comprehensible.

An interval_map is usable as a map, but it is also an aggregation
device. You may think of it a "counter" or "quantifier" for associated
"things" that can occur in time (e.g. count number of party guests).
Looking from this important use case it is often desirabel to omit
segments from the map, that are counted 0 times (in other words, that
are zero-quantified).

2011/5/25 Antal A. Buss <abuss_at_[hidden]>:
> Hi all,
>
> I'm trying to use interval_map to implement some kind of range to
> value directory, but I have some non expected results.
>
> The test code I'm using is:
> ------------------------
> #include <iostream>
> #include <boost/icl/interval_map.hpp>
> #include <boost/icl/discrete_interval.hpp>
>
> using namespace std;
> using namespace boost::icl;
>
> int main(int argc, char const **argv)
> {
>  interval_map<size_t, int> imap;
>  typedef discrete_interval<size_t> interval_t;
>
>  imap += make_pair(construct<interval_t>(0, 7, interval_bounds::closed()),0);
>  cout << "imap: " << imap << endl;
>
>  imap.set(make_pair(construct<interval_t>(0, 0, interval_bounds::closed()),1));
>  cout << "imap: " << imap << endl;
>
>  imap.erase(construct<interval_t>(3, 3, interval_bounds::closed()));
>  cout << "imap: " << imap << endl;
> }
> ------------------------
>
> The result I got is:
>  imap: {}
>  imap: {([0,0]->1)}
>  imap: {([0,0]->1)}
>
> but the result I was expecting is:
>  imap: {([0,7]->0)}
>  imap: {([0,0]->1)((0,7]->0)}
>  imap: {([0,0]->1)((0,3)->0)((3,7]->0)}

So again, from the perspective of counting or "quantification" both
results are equal, if we are not interested in zero-counted segments.
If we omit the zero-quantified segments in the second imap, it equals
the first one.

Thank you for the question. This is probably a trap for many users,
because it is different from the standard semantics of a std::map that
we tend to expect. From the perspective of most use cases of
interval_map as a means for aggregation though, the current
default-behavior seems to be justified.

HTH,
Joachim

-- 
Interval Container Library [Boost.Icl]
http://www.joachim-faulhaber.de