std::erase_if (std::unordered_map) - cppreference.com (original) (raw)
| | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------------------------------- | | template< class Key, class T, class Hash, class KeyEqual, class Alloc, class Pred > std::unordered_map<Key, T, Hash, KeyEqual, Alloc>::size_type erase_if( std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& c, Pred pred ); | | (since C++20) (constexpr since C++26) |
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();
[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 #include void println(auto rem, const auto& 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_map<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) { const auto& [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, e}, {4, d}, {3, c}, {2, b}, {1, a}} Erase items with odd keys: {{4, d}, {2, b}} 3 items removed.