std::erase_if (std::unordered_multimap)

 

C++

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list

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unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

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std::unordered_multimap

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

 

Defined in header <unordered_map>
template< class Key, class T, class Hash, class KeyEqual, class Alloc,           class Pred > std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>::size_type     erase_if( std::unordered_multimap<Key, T, 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_map>
 
void println(auto rem, auto const& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& [key, value] : container)
        std::cout << sep << '{' << key << ", " << value << '}', *sep = ',';
    std::cout << "}\n";
}
 
int main()
{
    std::unordered_multimap<int, char> data
    {
        {1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'},
        {5, 'e'}, {4, 'f'}, {5, 'g'}, {5, 'g'},
    };
    println("Original:\n", data);
 
    const auto count = std::erase_if(data, [](const auto& item)
    {
        auto const& [key, value] = item;
        return (key & 1) == 1;
    });
 
    println("Erase items with odd keys:\n", data);
    std::cout << count << " items removed.\n";
}

Possible output:

Original:
{{5, g}, {5, g}, {5, e}, {4, f}, {4, d}, {3, c}, {2, b}, {1, a}}
Erase items with odd keys:
{{4, f}, {4, d}, {2, b}}
5 items removed.

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)