How to Sort a Map by Values in C++ - Step by Step Examples

How to Sort a Map by Values in C++ ?

Answer

To sort a map by values in C++, you need to convert the map to a vector of pairs, sort the vector by values, and then optionally create a new map from the sorted vector. This method allows you to sort the map based on values.

✐ Examples

1 Sorting a Map by Values Using a Vector of Pairs

We can sort a map by values in C++ by converting the map to a vector of pairs, sorting the vector by values, and then optionally creating a new map from the sorted vector.

For example,

We start by including the <map>, <vector>, <algorithm>, and <iostream> headers, which provide the necessary functions and data structures for working with maps, vectors, sorting, and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We create a vector of pairs named mapVector and copy the key-value pairs from the map to the vector.
We sort the vector by values using the std::sort function with a custom comparator.
We print the sorted vector to the console using a range-based for loop and the std::cout function to verify the sorting.
Optionally, we create a new map from the sorted vector if needed.

C++ Program

#include <map>
#include <vector>
#include <algorithm>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<std::string, int> myMap = {
        {"apple", 3},
        {"banana", 1},
        {"cherry", 2}
    };

    // Create a vector of pairs and copy the key-value pairs from the map to the vector
    std::vector<std::pair<std::string, int>> mapVector(myMap.begin(), myMap.end());

    // Sort the vector by values
    std::sort(mapVector.begin(), mapVector.end(),
        [](const std::pair<std::string, int>& a, const std::pair<std::string, int>& b) {
            return a.second < b.second;
        });

    // Print the sorted vector
    std::cout << "Sorted Map by Values:\n";
    for (const auto& pair : mapVector) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    // Optionally, create a new map from the sorted vector
    std::map<std::string, int> sortedMap;
    for (const auto& pair : mapVector) {
        sortedMap[pair.first] = pair.second;
    }

    return 0;
}

Output

Sorted Map by Values:
banana: 1
cherry: 2
apple: 3

2 Sorting a Map by Values in Descending Order

We can sort a map by values in descending order in C++ by converting the map to a vector of pairs, sorting the vector by values in descending order, and then optionally creating a new map from the sorted vector.

For example,

We start by including the <map>, <vector>, <algorithm>, and <iostream> headers, which provide the necessary functions and data structures for working with maps, vectors, sorting, and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We create a vector of pairs named mapVector and copy the key-value pairs from the map to the vector.
We sort the vector by values in descending order using the std::sort function with a custom comparator.
We print the sorted vector to the console using a range-based for loop and the std::cout function to verify the sorting.
Optionally, we create a new map from the sorted vector if needed.

C++ Program

#include <map>
#include <vector>
#include <algorithm>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<std::string, int> myMap = {
        {"apple", 3},
        {"banana", 1},
        {"cherry", 2}
    };

    // Create a vector of pairs and copy the key-value pairs from the map to the vector
    std::vector<std::pair<std::string, int>> mapVector(myMap.begin(), myMap.end());

    // Sort the vector by values in descending order
    std::sort(mapVector.begin(), mapVector.end(),
        [](const std::pair<std::string, int>& a, const std::pair<std::string, int>& b) {
            return a.second > b.second;
        });

    // Print the sorted vector
    std::cout << "Sorted Map by Values (Descending):\n";
    for (const auto& pair : mapVector) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    // Optionally, create a new map from the sorted vector
    std::map<std::string, int> sortedMap;
    for (const auto& pair : mapVector) {
        sortedMap[pair.first] = pair.second;
    }

    return 0;
}

Output

Sorted Map by Values (Descending):
apple: 3
cherry: 2
banana: 1

3 Sorting a Map by Values with Integer Keys

We can sort a map with integer keys by values in C++ by converting the map to a vector of pairs, sorting the vector by values, and then optionally creating a new map from the sorted vector.

For example,

We start by including the <map>, <vector>, <algorithm>, and <iostream> headers, which provide the necessary functions and data structures for working with maps, vectors, sorting, and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We create a vector of pairs named mapVector and copy the key-value pairs from the map to the vector.
We sort the vector by values using the std::sort function with a custom comparator.
We print the sorted vector to the console using a range-based for loop and the std::cout function to verify the sorting.
Optionally, we create a new map from the sorted vector if needed.

C++ Program

#include <map>
#include <vector>
#include <algorithm>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, std::string> myMap = {
        {3, "three"},
        {1, "one"},
        {2, "two"}
    };

    // Create a vector of pairs and copy the key-value pairs from the map to the vector
    std::vector<std::pair<int, std::string>> mapVector(myMap.begin(), myMap.end());

    // Sort the vector by values
    std::sort(mapVector.begin(), mapVector.end(),
        [](const std::pair<int, std::string>& a, const std::pair<int, std::string>& b) {
            return a.second < b.second;
        });

    // Print the sorted vector
    std::cout << "Sorted Map by Values:\n";
    for (const auto& pair : mapVector) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    // Optionally, create a new map from the sorted vector
    std::map<int, std::string> sortedMap;
    for (const auto& pair : mapVector) {
        sortedMap[pair.first] = pair.second;
    }

    return 0;
}

Output

Sorted Map by Values:
1: one
2: two
3: three

Summary

In this tutorial, we learned How to Sort a Map by Values in C++ language with well detailed examples.

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How to Sort a Map by Values in C++ - Step by Step Examples