How to Filter a Map Based on Values in C++ - Step by Step Examples

How to Filter a Map Based on Values in C++ ?

Answer

To filter a map based on values in C++, you can iterate over the map and insert the key-value pairs that meet the filter criteria into a new map. This method allows you to create a subset of the original map based on specific value conditions.

✐ Examples

1 Filtering a Map Based on Value Range

We can filter a map based on a range of values in C++ by iterating over the map and inserting key-value pairs that fall within the specified range into a new map.

For example,

We start by including the <map> and <iostream> headers, which provide the necessary functions and data structures for working with maps 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 integer values.
We declare an empty map named filteredMap to store the filtered key-value pairs.
We define the lower and upper bounds of the value range.
We iterate over the original map using a range-based for loop and check if each value falls within the specified range.
We insert the key-value pairs that meet the condition into the filteredMap.
We print the filtered map to the console using a range-based for loop and the std::cout function to verify the filtering.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, int> myMap = {
        {1, 10},
        {2, 20},
        {3, 30},
        {4, 40},
        {5, 50}
    };

    // Declare an empty map to store the filtered key-value pairs
    std::map<int, int> filteredMap;

    // Define the value range
    int lowerBound = 20;
    int upperBound = 40;

    // Iterate over the original map and filter based on the value range
    for (const auto& pair : myMap) {
        if (pair.second >= lowerBound && pair.second <= upperBound) {
            filteredMap[pair.first] = pair.second;
        }
    }

    // Print the filtered map
    std::cout << "Filtered Map by Value Range:\n";
    for (const auto& pair : filteredMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

Filtered Map by Value Range:
2: 20
3: 30
4: 40

2 Filtering a Map Based on Specific Values

We can filter a map based on specific values in C++ by iterating over the map and inserting key-value pairs that match the specified values into a new map.

For example,

We start by including the <map> and <iostream> headers, which provide the necessary functions and data structures for working with maps 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 integer values.
We declare an empty map named filteredMap to store the filtered key-value pairs.
We define a set of specific values that we want to filter the map by.
We iterate over the original map using a range-based for loop and check if each value matches one of the specified values.
We insert the key-value pairs that meet the condition into the filteredMap.
We print the filtered map to the console using a range-based for loop and the std::cout function to verify the filtering.

C++ Program

#include <map>
#include <set>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, int> myMap = {
        {1, 10},
        {2, 20},
        {3, 30},
        {4, 40},
        {5, 50}
    };

    // Declare an empty map to store the filtered key-value pairs
    std::map<int, int> filteredMap;

    // Define the specific values to filter by
    std::set<int> valuesToFilter = {10, 30, 50};

    // Iterate over the original map and filter based on the specific values
    for (const auto& pair : myMap) {
        if (valuesToFilter.find(pair.second) != valuesToFilter.end()) {
            filteredMap[pair.first] = pair.second;
        }
    }

    // Print the filtered map
    std::cout << "Filtered Map by Specific Values:\n";
    for (const auto& pair : filteredMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

Filtered Map by Specific Values:
1: 10
3: 30
5: 50

3 Filtering a Map with String Values Based on Prefix

We can filter a map with string values based on a specific prefix in C++ by iterating over the map and inserting key-value pairs that have values starting with the given prefix into a new map.

For example,

We start by including the <map> and <iostream> headers, which provide the necessary functions and data structures for working with maps 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 declare an empty map named filteredMap to store the filtered key-value pairs.
We define a prefix string that we want to filter the map by.
We iterate over the original map using a range-based for loop and check if each value starts with the specified prefix.
We insert the key-value pairs that meet the condition into the filteredMap.
We print the filtered map to the console using a range-based for loop and the std::cout function to verify the filtering.

C++ Program

#include <map>
#include <iostream>

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

    // Declare an empty map to store the filtered key-value pairs
    std::map<int, std::string> filteredMap;

    // Define the prefix to filter by
    std::string prefix = "ap";

    // Iterate over the original map and filter based on the prefix
    for (const auto& pair : myMap) {
        if (pair.second.find(prefix) == 0) {
            filteredMap[pair.first] = pair.second;
        }
    }

    // Print the filtered map
    std::cout << "Filtered Map by Prefix:\n";
    for (const auto& pair : filteredMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

Filtered Map by Prefix:
1: apple
3: apricot

Summary

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

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How to Filter a Map Based on Values in C++ - Step by Step Examples