std::erase_if (std::unordered_set)

 

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std::unordered_set

Member types
Member functions
unordered_set::unordered_set unordered_set::~unordered_set unordered_set::operator= unordered_set::get_allocator Iterators unordered_set::beginunordered_set::cbegin unordered_set::endunordered_set::cend Capacity unordered_set::size unordered_set::max_size unordered_set::empty Modifiers unordered_set::clear unordered_set::erase unordered_set::swap unordered_set::extract (C++17) unordered_set::merge (C++17) unordered_set::insert unordered_set::insert_range (C++23)   unordered_set::emplace unordered_set::emplace_hint	Lookup unordered_set::count unordered_set::find unordered_set::contains (C++20) unordered_set::equal_range Bucket interface unordered_set::begin(size_type)unordered_set::cbegin(size_type) unordered_set::end(size_type)unordered_set::cend(size_type) unordered_set::bucket_count unordered_set::max_bucket_count unordered_set::bucket_size unordered_set::bucket Hash policy unordered_set::load_factor unordered_set::max_load_factor unordered_set::rehash unordered_set::reserve Observers unordered_set::hash_function unordered_set::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_set) erase_if(std::unordered_set) (C++20)
Deduction guides (C++17)

 

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();

Parameters

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

Return value

The number of erased elements.

Complexity

Linear.

Example

Run this code

#include <iostream>
#include <unordered_set>
 
void println(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};
    println("Original:\n", data);
 
    auto divisible_by_3 = [](auto const& x) { return (x % 3) == 0; };
 
    const auto count = std::erase_if(data, divisible_by_3);
 
    println("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.

See also

removeremove_if	removes elements satisfying specific criteria (function template)
ranges::removeranges::remove_if (C++20)(C++20)	removes elements satisfying specific criteria (niebloid)