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std::erase_if (std::unordered_set)

From cppreference.com
 
 
 
 
Defined in header <unordered_set>
template< class Key, class Hash, class KeyEqual, class Alloc,

          class Pred >
std::unordered_set<Key, Hash, KeyEqual, Alloc>::size_type
    erase_if( std::unordered_set<Key, Hash, KeyEqual, Alloc>& c,

              Pred pred );
(since C++20)

Erases all elements that satisfy the predicate pred from c.

Equivalent to

auto old_size = c.size();
for (auto first = c.begin(), last = c.end(); first != last;)
{
    if (pred(*first))
        first = c.erase(first);
    else
        ++first;
}
return old_size - c.size();

Contents

[edit] Parameters

c - container from which to erase
pred - predicate that returns true if the element should be erased

[edit] Return value

The number of erased elements.

[edit] Complexity

Linear.

[edit] Example

#include <iostream>
#include <unordered_set>
 
void print(auto rem, auto const& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& item : container)
        std::cout << sep << item, *sep = ',';
    std::cout << "}\n";
}
 
int main()
{
    std::unordered_set data{3, 3, 4, 5, 5, 6, 6, 7, 2, 1, 0};
    print("Original:\n", data);
 
    auto divisible_by_3 = [](auto const& x) { return (x % 3) == 0; };
 
    const auto count = std::erase_if(data, divisible_by_3);
 
    print("Erase all items divisible by 3:\n", data);
    std::cout << count << " items erased.\n";
}

Possible output:

Original:
{0, 1, 2, 7, 6, 5, 4, 3}
Erase all items divisible by 3:
{1, 2, 7, 5, 4}
3 items erased.

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]