How to Remove Duplicates in a Vector in C++ - Step by Step Examples

How to Remove Duplicates in a Vector in C++ ?

Answer

To remove duplicates from a vector in C++, you can use the std::sort and std::unique algorithms from the Standard Library, or you can use a std::unordered_set to keep only unique elements.

✐ Examples

1 Remove All Duplicates from a Vector Using std::unordered_set

In this example,

We start by including the necessary headers: <vector>, <unordered_set>, and <iostream>.
We create a vector named vec and initialize it with some integer values, including duplicates.
Next, we create an std::unordered_set named set and initialize it with the elements of vec. The unordered_set only keeps unique elements.
We then create a new vector named unique_vec and initialize it with the elements of the set. This ensures that unique_vec contains only unique elements from the original vector.
Finally, we print the new vector to standard output to see the result.

C++ Program

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

int main() {
    std::vector&lt;int&gt; vec = {1, 2, 2, 3, 4, 4, 4, 5, 6, 6};
    std::unordered_set&lt;int&gt; set(vec.begin(), vec.end());
    std::vector&lt;int&gt; unique_vec(set.begin(), set.end());
    std::cout &lt;&lt; "Vector after removing all duplicates: ";
    for (const int &val : unique_vec) {
        std::cout &lt;&lt; val &lt;&lt; " ";
    }
    std::cout &lt;&lt; std::endl;
    return 0;
}

Output

Vector after removing all duplicates: 1 2 3 4 5 6

2 Remove Consecutive Duplicates from a Sorted Vector

In this example,

We start by including the necessary headers: <vector>, <algorithm>, and <iostream>.
We create a vector named vec and initialize it with some integer values, including consecutive duplicates.
Next, we use the std::sort algorithm to sort the vector. This step is crucial because std::unique only removes consecutive duplicates, so the vector must be sorted first.
We then use the std::unique algorithm to remove consecutive duplicates. This algorithm returns an iterator pointing to the new logical end of the vector.
We resize the vector to remove the undefined elements left at the end after using std::unique by passing the iterator returned by std::unique to the erase method.
Finally, we print the modified vector to standard output 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 = {1, 2, 2, 3, 4, 4, 4, 5, 6, 6};
    std::sort(vec.begin(), vec.end());
    auto it = std::unique(vec.begin(), vec.end());
    vec.erase(it, vec.end());
    std::cout &lt;&lt; "Vector after removing duplicates: ";
    for (const int &val : vec) {
        std::cout &lt;&lt; val &lt;&lt; " ";
    }
    std::cout &lt;&lt; std::endl;
    return 0;
}

Output

Vector after removing duplicates: 1 2 3 4 5 6

Summary

In this tutorial, we learned How to Remove Duplicates in a Vector in C++ language with well detailed examples.

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How to Remove Duplicates in a Vector in C++ - Step by Step Examples

How to Remove Duplicates in a Vector in C++ ?

Answer

✐ Examples

1 Remove All Duplicates from a Vector Using std::unordered_set

C++ Program

Output

2 Remove Consecutive Duplicates from a Sorted Vector

C++ Program

Output

Summary

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