class Pred >
std::unordered_map<Key, T, Hash, KeyEqual, Alloc>::size_type
erase_if( std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& c,
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] ComplexityLinear.
[edit] Example#include <iostream>
#include <unordered_map>
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.[edit] See also
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