Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.
PrevUpHomeNext

Std transform

Instead of writing loops, the standard algorithm std::transform can be used to fill interval containers from std containers of user defined objects. We need a function, that maps the user defined object into the segement type of an interval map or the interval type of an interval set. Based on that we can use std::transform with an icl::inserter or icl::adder to transform the user objects into interval containers.

#include <iostream>
#include <vector>
#include <algorithm>
#include <boost/icl/split_interval_map.hpp>
#include <boost/icl/separate_interval_set.hpp>

using namespace std;
using namespace boost;
using namespace boost::icl;

// Suppose we are working with a class called MyObject, containing some
// information about interval bounds e.g. _from, _to and some data members
// that carry associated information like e.g. _value.
class MyObject
{
public:
    MyObject(){}
    MyObject(int from, int to, int value): _from(from), _to(to), _value(value){}
    int from()const {return _from;}
    int to()const   {return _to;}
    int value()const{return _value;}
private:
    int _from;
    int _to;
    int _value;
};

// ... in order to use the std::transform algorithm to fill
// interval maps with MyObject data we need a function
// 'to_segment' that maps an object of type MyObject into
// the value type to the interval map we want to tranform to ...
pair<discrete_interval<int>, int> to_segment(const MyObject& myObj)
{
    return std::pair< discrete_interval<int>, int >
        (discrete_interval<int>::closed(myObj.from(), myObj.to()), myObj.value());
}

// ... there may be another function that returns the interval
// of an object only
discrete_interval<int> to_interval(const MyObject& myObj)
{
    return discrete_interval<int>::closed(myObj.from(), myObj.to());
}


// ... make_object computes a sequence of objects to test.
vector<MyObject> make_objects()
{
    vector<MyObject> object_vec;
    object_vec.push_back(MyObject(2,3,1));
    object_vec.push_back(MyObject(4,4,1));
    object_vec.push_back(MyObject(1,2,1));
    return object_vec;
}

// ... show_objects displays the sequence of input objects.
void show_objects(const vector<MyObject>& objects)
{
    vector<MyObject>::const_iterator iter = objects.begin();
    while(iter != objects.end())
    {
        cout << "([" << iter->from() << "," << iter->to() << "]," 
             << iter->value() << ")";
        ++iter;
    }
}


void std_transform()
{
    // This time we want to transform objects into a splitting interval map:
    split_interval_map<int,int> segmap;
    vector<MyObject> myObjects = make_objects();

    // Display the input
    cout << "input sequence: "; show_objects(myObjects); cout << "\n\n";

    // Use an icl::inserter to fill the interval map via inserts
    std::transform(myObjects.begin(), myObjects.end(),
                   icl::inserter(segmap, segmap.end()),
                   to_segment);
    cout << "icl::inserting: " << segmap << endl;
    segmap.clear();

    // In order to compute aggregation results on associated values, we
    // usually want to use an icl::adder instead of an std or icl::inserter
    std::transform(myObjects.begin(), myObjects.end(),
                   icl::adder(segmap, segmap.end()),
                   to_segment);
    cout << "icl::adding   : " << segmap << "\n\n";

    separate_interval_set<int> segset;
    std::transform(myObjects.begin(), myObjects.end(),
                   icl::adder   (segset, segset.end()),
    // could be a  icl::inserter(segset, segset.end()), here: same effect 
                   to_interval);

    cout << "Using std::transform to fill a separate_interval_set:\n\n";
    cout << "icl::adding   : " << segset << "\n\n";
}


int main()
{
    cout << ">>  Interval Container Library: Example std_transform.cpp  <<\n";
    cout << "------------------------------------------------------------\n";
    cout << "Using std::transform to fill a split_interval_map:\n\n";

    std_transform();
    return 0;
}

// Program output:
/*----------------------------------------------------------
>>  Interval Container Library: Example std_transform.cpp  <<
------------------------------------------------------------
Using std::transform to fill a split_interval_map:

input sequence: ([2,3],1)([4,4],1)([1,2],1)

icl::inserting: {([1,2)->1)([2,3]->1)([4,4]->1)}
icl::adding   : {([1,2)->1)([2,2]->2)((2,3]->1)([4,4]->1)}

Using std::transform to fill a separate_interval_set:

icl::adding   : {[1,3][4,4]}
----------------------------------------------------------*/

To get clear about the different behaviors of interval containers in the example, you may want to refer to the section about interval combining styles that uses the same data.


PrevUpHomeNext