STL Tips : std::remove(_if)

STL

std::remove / std::remove_if / std::erase

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#include <algorithm>

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Can STL Algorithms Add/Remove From Containers?

No.

• STL algorithms do not directly add/remove.
• Because STL algorithms work on iterators, which give access to the elements of the container.

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What about std::remove, std::remove_if, std::unique?

• They don’t erase elements from the container.
• Instead, they rearrange the elements you want to remove to the end.
• Return the iterator to the new logical end.
• If you really want to erase the element, then you then need to call container’s erase.

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Example 01: Delete element from vector with vector’s erase.

std::vector<int> v = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

// Removes 5.
v.erase(std::remove(v.begin(), v.end(), 5), v.end());
// Output : 0 1 2 3 4 6 7 8 9

// Removes all odd numbers.
v.erase(std::remove_if(v.begin(), v.end(), [](int val) { return val & 1; }), v.end());
// Output : 0 2 4 6 8

Try here.

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Example 02:

int main() 
{
    std::vector<int> v = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    
    auto end = std::remove(v.begin(), v.end(), 3);

    int count = std::distance(v.begin(), end) + std::distance(end, v.end());

    if ( count == v.size() )
    {
        std::cout << "EQUAL\n" ;
    }
}

Try here.

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Example 03: Delete element from vector with std::erase (with C++20)

int main() 
{
    std::vector<int> v = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    
    std::erase(v, 3);

    std::cout << v.size() << '\n';
}

Try here.

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Example 04 : Remove vowels from a string

std::string text = "Hello. This is a test string.\n";

text.erase(
    std::remove_if(text.begin(), text.end(), [](char c) {
        std::string vowels = "aeiouAEIOU";
        return vowels.find(c) != std::string::npos;
    }),
    text.end()
);

std::cout << "String without vowels: " << text << std::endl;

Try here.

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Example 05 : Remove vowels from a string (with C++20)

std::string text = "Hello. This is a test string.\n";

std::erase_if(text, [](char c) {
    std::string vowels = "aeiouAEIOU";
    return vowels.find(c) != std::string::npos;
});

std::cout << text << std::endl;

Try here.