How to Filter Items of a Set based on a Condition in C++ - Step by Step Examples

How to Filter Items of a Set based on a Condition in C++ ?

Answer

To filter items of a set based on a condition in C++, you can use the std::copy_if algorithm with a lambda function as the filtering predicate to create a new set from the filtered items.

✐ Examples

1 Filtering Numbers Greater Than 5

In this example,

We create a set named numberSet using the std::unordered_set container, which contains integer values 1, 5, 10, 15, and 20.
We define a new set named filteredSet of the same type and size as numberSet.
We use the std::copy_if algorithm with a lambda function as the filtering predicate to copy the numbers greater than 5 from numberSet to filteredSet.
Finally, we iterate through filteredSet and print each filtered item to the console.

C++ Program

#include <iostream>
#include <unordered_set>
#include <algorithm>

int main() {
    std::unordered_set<int> numberSet = {1, 5, 10, 15, 20};
    std::unordered_set<int> filteredSet(numberSet.size());
    
    std::copy_if(numberSet.begin(), numberSet.end(), filteredSet.begin(), [](int num) { return num > 5; });
    
    for (int num : filteredSet) {
        std::cout << num << std::endl;
    }
    
    return 0;
}

Output

10
15
20

2 Filtering Strings Containing 'a'

In this example,

We create a set named stringSet using the std::unordered_set container, which contains string values "apple", "banana", "cherry", "date", and "grape".
We define a new set named filteredStringSet of the same type and size as stringSet.
We use the std::copy_if algorithm with a lambda function as the filtering predicate to copy the strings containing the letter 'a' from stringSet to filteredStringSet.
Finally, we iterate through filteredStringSet and print each filtered string to the console.

C++ Program

#include <iostream>
#include <unordered_set>
#include <algorithm>
#include <string>

int main() {
    std::unordered_set<std::string> stringSet = {"apple", "banana", "cherry", "date", "grape"};
    std::unordered_set<std::string> filteredStringSet(stringSet.size());
    
    std::copy_if(stringSet.begin(), stringSet.end(), filteredStringSet.begin(), [](const std::string& str) { return str.find('a') != std::string::npos; });
    
    for (const std::string& str : filteredStringSet) {
        std::cout << str << std::endl;
    }
    
    return 0;
}

Output

apple
banana
grape

Summary

In this tutorial, we learned How to Filter Items of a Set based on a Condition in C++ language with well detailed examples.

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