How to Remove Items from Vector based on a Condition in C++ - Step by Step Examples

How to Remove Items from Vector based on a Condition in C++ ?

Answer

To remove items from a vector based on a condition in C++, you can use the erase method along with the remove_if algorithm.


✐ Examples

1 Remove Items Using remove_if and erase

In this example,

  1. We start by including the necessary headers: <vector> and <algorithm>.
  2. We create a vector named vec and initialize it with some integer values.
  3. We define a predicate function named isLessThan30 that returns true if the passed element is less than 30.
  4. We use the remove_if algorithm to shift all elements that satisfy the condition specified by the predicate function to the end of the vector.
  5. We use the erase method to remove the elements from the end to the actual end of the vector.
  6. Finally, we print the modified vector to see the result.

C++ Program

#include &lt;vector&gt;
#include &lt;algorithm&gt;
#include &lt;iostream&gt;

bool isLessThan30(int x) {
    return x &lt; 30;
}

int main() {
    std::vector&lt;int&gt; vec = {10, 20, 30, 40, 50};
    vec.erase(std::remove_if(vec.begin(), vec.end(), isLessThan30), vec.end());
    std::cout &lt;&lt; "Vector after removing items based on condition: ";
    for (int val : vec) {
        std::cout &lt;&lt; val &lt;&lt; " ";
    }
    std::cout &lt;&lt; std::endl;
    return 0;
}

Output

Vector after removing items based on condition: 30 40 50

2 Remove Items Using Lambda Function

In this example,

  1. We start by including the necessary headers: <vector> and <algorithm>.
  2. We create a vector named vec and initialize it with some integer values.
  3. We use a lambda function as a predicate to specify the condition for removing elements. In this example, we want to remove elements less than 30.
  4. We use the remove_if algorithm with the lambda function to shift all elements that satisfy the condition to the end of the vector.
  5. We use the erase method to remove the elements from the end to the actual end of the vector.
  6. Finally, we print the modified vector to see the result.

C++ Program

#include &lt;vector&gt;
#include &lt;algorithm&gt;
#include &lt;iostream&gt;

int main() {
    std::vector&lt;int&gt; vec = {10, 20, 30, 40, 50};
    vec.erase(std::remove_if(vec.begin(), vec.end(), [](int x) { return x &lt; 30; }), vec.end());
    std::cout &lt;&lt; "Vector after removing items based on condition: ";
    for (int val : vec) {
        std::cout &lt;&lt; val &lt;&lt; " ";
    }
    std::cout &lt;&lt; std::endl;
    return 0;
}

Output

Vector after removing items based on condition: 30 40 50

Summary

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


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