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

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

Answer

To filter items of a vector based on a condition in C++, you can use the `std::remove_if` algorithm provided by the algorithm header in combination with the erase-remove idiom.

✐ Examples

1 Filter Items Greater Than a Threshold

In this example,

First, you define a vector containing the elements you want to filter.
Next, you specify the condition for filtering, such as greater than a threshold, using a lambda function or a functor.
Then, you use the `std::remove_if` algorithm with the specified condition to move the elements that satisfy the condition to the end of the vector.
Finally, you erase the elements from the end of the vector to remove them.

C++ Program

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

int main() {
    // Define a vector containing elements
    std::vector<int> vec = {1, 5, 10, 15, 20};

    // Specify the threshold for filtering
    int threshold = 10;

    // Define a lambda function to filter elements greater than the threshold
    auto condition = [threshold](int x) { return x > threshold; };

    // Use std::remove_if algorithm with the condition
    vec.erase(std::remove_if(vec.begin(), vec.end(), condition), vec.end());

    // Print the filtered vector
    for (int i : vec) {
        std::cout << i << " ";
    }
    std::cout << std::endl;
    return 0;
}

Output

15 20

2 Filter Items Meeting a Condition

In this example,

Define a vector containing elements.
Specify the condition for filtering using a lambda function or a functor.
Use the `std::remove_if` algorithm with the specified condition to move the elements meeting the condition to the end of the vector.
Erase the elements from the end of the vector to remove them.

C++ Program

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

int main() {
    // Define a vector containing elements
    std::vector<int> vec = {1, 5, 10, 15, 20};

    // Specify the condition for filtering
    auto condition = [](int x) { return x % 2 == 0; }; // Select even numbers

    // Use std::remove_if algorithm with the condition
    vec.erase(std::remove_if(vec.begin(), vec.end(), condition), vec.end());

    // Print the filtered vector
    for (int i : vec) {
        std::cout << i << " ";
    }
    std::cout << std::endl;
    return 0;
}

Output

1 5 15

Summary

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

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

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

Answer

✐ Examples

1 Filter Items Greater Than a Threshold

C++ Program

Output

2 Filter Items Meeting a Condition

C++ Program

Output

Summary

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