How to use find for the inner map

[jo123]

Hello Everyone,
I need a help in using "find" for the inner map.
My 2D map is like this

  std::map<int, pair<int, double> > my2DMap;

and I am using "find" for the outer map like below and it works fine:

my2DMap.insert(pair<int, pair<int, double> >(x, pair<int, double>(y, z)));

std::map<int, pair<int, double> >::iterator itv = my2DMap.find(x);
if (itv == my2DMap.end()){
........
}

But I am not able to use "find" for the inner map to search for "y".
Is there any way I can use "find" to search the integer "y" without using an additional map for the inner key-value pair (int-double in my case)?

Thanks.

[keskiverto]

That is not a "2D map". Each key has exactly one value. For key "x", the value either has "y" as the integer component, or does not.

How about std::map<pair<int,int>, double>

[gunnerfunner]

You can reach the "inner map" or the value element of the key-value pair in the following way:

#include <iostream>
#include <map>
#include <tuple>

int main()
{
    std::map<int, std::pair<int, double> > my2DMap;

    my2DMap.insert (std::make_pair(1, std::make_pair(2, 3.4)));
    my2DMap.insert (std::make_pair(5, std::make_pair(6, 7.8)));

    auto elem = my2DMap.find(5);

    if(elem != my2DMap.end())
    {
       std::cout << elem -> second.second << '\n';
    }
    else
    {
        std::cout << "Key not found \n";
    }
}

[jo123]

Thanks Keskiverto.
I tried like how you mentioned as below, but it is searching the whole pair of (x, y):

myMap.insert(std::make_pair(std::make_pair(x, y), z));
    
auto elem = myMap.find(std::make_pair(x, y));

But I want to find first int (x), if it is available, find the next int (y), if that is available then update the value of the double (z). If int (y) is not found then insert (y, z) into the map.
If x is not available then insert (x,y,z) into the map.
Something like this:

if (myMap.find(x) = true)
{
    if (myMap.find(y) = true)
    {
        update z;
    }
    else
    {
        insert (y, z);
    }
}
else
{
insert (x, y, z);
}

Thanks Gunnerfunner. I am struggling to find the next int in the inner pair (2 or 6 in the example you have showed). How can I find it?

Many thanks.

[gunnerfunner]

http://stackoverflow.com/questions/4367892/search-for-specific-value-in-stdmap

[gunnerfunner]

#include <iostream>
#include <map>
#include <tuple>

int main()
{
    std::map<int, std::pair<int, double> > my2DMap;

    my2DMap.insert (std::make_pair(1, std::make_pair(2, 3.4)));
    my2DMap.insert (std::make_pair(5, std::make_pair(6, 7.8)));

    int searchVal = 9;
    bool match = false;

    for (auto itr = my2DMap.begin(); itr != my2DMap.end(); itr++)
    {
        if(itr->second.first == searchVal)
        {
            std::cout << "Key is: " << itr->first << " and int's double pair is: " << itr->second.second << '\n';
            match = true;
        }
    }
    if (match == false)
    {
        std::cout << "Not found\n";
    }
}

[jo123]

Thank you so much Gunnerfunner.

[keskiverto]

But I want to find first int (x), if it is available, find the next int (y), if that is available then update the value of the double (z). If int (y) is not found then insert (y, z) into the map.

Indeed.

#include <iostream>
#include <map>

int main()
{
    std::map<std::pair<int, int>, double> my2DMap;

    // these insert
    my2DMap[ std::make_pair(1, 2) ] = 3.4;
    my2DMap[ std::make_pair(5, 6) ] = 7.8;

    for ( auto & itr : my2DMap ) {
        std::cout << "x=" << itr.first.first << " y="  << itr.first.second << " z=" << itr.second << '\n';
    }
    std::cout << '\n'; 

    // this updates
    my2DMap[ std::make_pair(1, 2) ] = 4.2;
    
    for ( auto & itr : my2DMap ) {
        std::cout << "x=" << itr.first.first << " y="  << itr.first.second << " z=" << itr.second << '\n';
    }
}

[jo123]

Thanks a lot Keskiverto.