Selection in the codomain of interval_map - c++

Question

In my current project processes, distinguishable intervals, needs to be combined, if they are adjacent.
For this purpose I wanted to use the fantastic boost::icl library. Every process can be uniquely identified by its id.
First I'm adding some intervals to my interval_map. Now I wanted to accomplish two things:
Iterate over all occurring process-types (Here id=1,4,7)
Secondly, iterate over all processes being in a certain subset of kinds, in such a way that merging of overlapping intervals is automatically done.
This is what I got so far:
#include <iostream>
#include <set>
#include <boost/icl/interval_map.hpp>
#include "boost/icl/closed_interval.hpp"
struct Process {
int id;
};
bool operator==(const Process& p, const Process& q) {
return p.id == q.id;
}
bool operator<(const Process& p, const Process& q) {
return p.id < q.id;
}
std::ostream& operator<<(std::ostream& str, const Process& p) {
str << "Process{" << p.id << "}";
return str;
}
int main(int, char**) {
using namespace boost::icl;
interval_map<double, std::set<Process>> imap;
imap.add({ interval<double>::closed(0., 4.),{ Process{ 4 } } });
imap.add({ interval<double>::closed(2., 6.),{ Process{ 1 } } });
imap.add({ interval<double>::closed(4., 9.),{ Process{ 4 } } });
imap.add({ interval<double>::closed(8., 8.),{ Process{ 7 } } });
for (auto&& iter : imap) {
std::cout << iter.first << " - " << iter.second<< std::endl;
}
for (auto iter : find(imap, { Process{4} })) { // How to implement find on codomain
// Should print:
// [0.,4.] - { Process{4}}
// [4.,9.] - { Process{4}}
std::cout << iter.first << " - " << iter.second << std::endl;
}
}

Answer 1

First, an observation, since the intervals are closed, [0,4] and [4,6] aren't actually adjacent, but overlapping. Did you mean right_open?
Second, the interval map models a function, the mapping is not guaranteed to be injective.
In the limited scope of your example, it seems you'd rather invert the datastructure, to arrive at:
#include "boost/icl/closed_interval.hpp"
#include <boost/icl/interval_map.hpp>
#include <iostream>
#include <set>
#include <map>
struct Process {
int id;
friend bool operator==(const Process& p, const Process& q) { return p.id == q.id; }
friend bool operator<(const Process& p, const Process& q) { return p.id < q.id; }
friend std::ostream& operator<<(std::ostream& str, const Process& p) {
return str << "Process{" << p.id << "}";
}
};
int main(int, char**) {
using namespace boost::icl;
using Map = std::map<Process, boost::icl::interval_set<double> >; // instead of boost::icl::interval_map<double, std::set<Process> >;
using IVal = Map::mapped_type::interval_type;
Map imap;
imap[{4}] += IVal::right_open(0, 4);
imap[{1}] += IVal::right_open(2, 6);
imap[{4}] += IVal::right_open(4, 9);
imap[{7}] += IVal::closed(8, 8);
//for (auto&& el : imap) { std::cout << el.first << " - " << el.second << std::endl; }
Process key{4};
std::cout << key << " - " << imap[key];
}
This results in:
Process{4} - {[0,9)}
Which is what I think you meant with "in such a way that merging of overlapping intervals is automatically done".
Having Both
Of course you can derive the inverse mappings from the original data-structure:
template <typename IMap>
auto inverted(IMap const& imap) {
std::map<typename IMap::codomain_type::value_type, boost::icl::interval_set<typename IMap::domain_type> > output;
for (auto& el : imap)
for (auto& key: el.second)
output[key] += el.first;
return output;
}
See it Live On Coliru
#include "boost/icl/closed_interval.hpp"
#include <boost/icl/interval_map.hpp>
#include <iostream>
#include <set>
struct Process {
int id;
friend bool operator==(const Process& p, const Process& q) { return p.id == q.id; }
friend bool operator<(const Process& p, const Process& q) { return p.id < q.id; }
};
std::ostream& operator<<(std::ostream& str, const Process& p) {
str << "Process{" << p.id << "}";
return str;
}
template <typename IMap>
auto inverted(IMap const& imap) {
std::map<typename IMap::codomain_type::value_type, boost::icl::interval_set<typename IMap::domain_type> > output;
for (auto& el : imap)
for (auto& key: el.second)
output[key] += el.first;
return output;
}
int main(int, char**) {
using namespace boost::icl;
using IMap = boost::icl::interval_map<double, std::set<Process> >;
using IVal = IMap::interval_type;
IMap imap;
imap.add({ IVal::right_open(0, 4), {Process{ 4 }} });
imap.add({ IVal::right_open(2, 6), {Process{ 1 }} });
imap.add({ IVal::right_open(4, 9), {Process{ 4 }} });
imap.add({ IVal::closed(8, 8), {Process{ 7 }} });
std::cout << imap << "\n\n";
for (auto&& iter : imap) {
std::cout << iter.first << " - " << iter.second << std::endl;
}
Process key{4};
std::cout << key << " - " << inverted(imap)[key] << "\n";
}
More Notes
Querying multiple keys in the domain is directly supported, see a good assortion of pointers here:
split_interval_map usage, efficient find all interval intersecting a point
boost multi_index_container search for records that fall within intervals defined by two fields
You can always construct your own data-structure that affords bi-directional indexes, such as shown e.g.
here boost::multi_index_container, operations on std::set inside container