C++ How to create a map from two other maps - c++

Question

How to create map MyMap3 as:
std::map< vector<std::pair<int, int>>, int > MyMap3
Example:
MyMap3[0] = ((1,3) , (1,5), 7 ) // 5 = 4 + 3
MyMap3[1] = ( (2,1) , (2,4), 6 ) // 6 = 1 + 5
Where the key = (vector of pairs) extract from 'MyMap1',
and the value = the sum of the pairs' values in 'MyMap2'.
I also don't care about the pair order, (2,4) is the same as (4,2)
std::map <int, vector<pair<int, int>> > MyMap1;
std::map< std::pair< int, int>, int> MyMap2;
Here is an Example:
MyMap1[0] = (0, (1,3) , (1,5) )
MyMap1[1] = (1, (2,1) , (2,4) )
MyMap2[0] = ( (1,3) , 4 )
MyMap2[1] = ( (1,5) , 3 )
MyMap2[2] = ( (2,1) , 1 )
MyMap2[3] = ( (4,2) , 5 )
I don't know how to do that, and this is my try:
std::map <int, vector<pair<int, int>> > ::iterator it1 = MyMap1.begin();
std::map<std::pair< int, int>, int> ::iterator it2 = MyMap2.begin();
// std::map< vector<pair<int, int> >, int> MyMap3;
std::map< pair<int, int> , int> MyMap3;
int i = 0;
while (it1 != MyMap1.end())
{
vector< pair<int, int> > temp = MyMap1[i];
vector< pair<int, int> > ::iterator it3 = temp.begin();
while (it3 != temp.end())
{
int a = it2->first.first;
int b = it2->first.second;
while (it2 != MyMap2.end())
{
if (it3 == MyMap2.find(std::make_pair(a, b))
MyMap3[std::make_pair(a, b)] += it2->second;
else
++it2;
}
++it3;
++i;
}
++it1;
}
I have syntax error in:
if (it3 == MyMap2.find(make_pair(a, b)))
MyMap3[std::make_pair(a, b)] += it2->second;

Answer 1

Your question is confuse, i decipher you want for each key in map1 to sum the value of each pair in the vector found in the map2 to a single value, and store the result with the map1 key. Not really what your code do…
Example result : http://coliru.stacked-crooked.com/a/a4d77c77fa6896c1
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <utility>
using Map1 = std::map< int, std::vector<std::pair<int,int>>>;
using Map2 = std::map< std::pair<int,int>, int >;
using Map3 = std::map< int, int >;
Map3 foo( Map1 const & m1, Map2 const & m2 ) {
auto m2end = m2.end(); // a constant call is move outside the loop
Map3 result;
for( auto & v1 : m1 ) { // each entry in m1 is made of the key as first and the value as second
for( auto & p1 : v1.second ) { // iterate over the vector of pair
auto v2it = m2.find( p1 ); // search for the pair
if ( v2it != m2end ) {
result[v1.first] += v2it->second; // if the pair was found, add the value for it to the result, using the map1 key as key
}
}
}
return result;
}
template<typename T,typename S>
std::ostream& operator<<(std::ostream& os, const std::pair<T,S>& pair )
{
os << "{ " << pair.first << ", " << pair.second << " }";
return os;
}
template<typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec)
{
os << "( ";
for (auto& el : vec)
{
os << el << ", ";
}
os << " )";
return os;
}
template<typename T,typename S>
std::ostream& operator<<(std::ostream& os, const std::map<T,S>& map)
{
for (auto& el : map)
{
os << el.first << " : " << el.second << "\n";
}
return os;
}
int main()
{
Map1 m1 { { 0, { {1,3}, {1,5}} }, { 1, { {2,1}, {2,4}} }, };
Map2 m2 { { {1,3}, 4 }, { {1,5}, 3 }, { {2,1}, 1 }, { {2,4}, 5 }, };
auto m3 = foo( m1, m2);
std::cout << "m1 :\n" << m1 << std::endl;
std::cout << "m2 :\n" << m2 << std::endl;
std::cout << "m3 :\n" << m3 << std::endl;
}