std::experimental::erase_if (std::unordered_map)

From cppreference.com

Defined in header <experimental/unordered_map>
template< class Key, class T, class Hash, class KeyEqual, class Alloc, class Pred >
void erase_if( std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& c, Pred pred );
(library fundamentals TS v2)

Erases all elements that satisfy the predicate pred from the container. Equivalent to

for (auto i = c.begin(), last = c.end(); i != last;)
{
    if (pred(*i))
        i = c.erase(i);
    else
        ++i;
}

Parameters

c - container from which to erase
pred - predicate that determines which elements should be erased

Complexity

Linear.

Example

#include <experimental/unordered_map>
#include <iostream>
 
template<typename Os, typename Container>
inline Os& operator<<(Os& os, Container const& cont)
{
    os << "{";
    for (const auto& item : cont)
        os << "{" << item.first << ", " << item.second << "}";
    return os << "}";
}
 
int main()
{
    std::unordered_map<int, char> data {{1, 'a'},{2, 'b'},{3, 'c'},{4, 'd'},
                                        {5, 'e'},{4, 'f'},{5, 'g'},{5, 'g'}};
    std::cout << "Original:\n" << data << '\n';
    std::experimental::erase_if(data, [](const auto& item)
    {
        return (item.first & 1) == 1;
    });
    std::cout << "Erase items with odd keys:\n" << data << '\n';
}

Possible output:

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

See also

removes elements satisfying specific criteria
(function template)