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My map:

std::map<std::array<byte, 16>, int> possible; // key is a byte array, value is a frequency of occurrence

I already filled the map. Now I need to remove the arrays that occurred once. It is necessary to remove from the map such pairs, the value of which is equal to one. How to do it?

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2 Answers 2

Reset to default
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Use erase_if:

const auto count = std::erase_if(possible, [](const auto& item) { auto const& [key, value] = item; return value == 1; });
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Prior to C++20, you will have to use map::erase() in a loop instead.
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std::map isn't designed to find elements by value, only by key. So, to do what you are asking for, you will have to manually loop through the map calling map::erase() on the desired items, eg:

auto iter = possible.begin(); while (iter != possible.end()) { if (iter->second == 1) { iter = possible.erase(iter); } else { ++iter; } }

In C++20 and later, you can use the std::map overload of std::erase_if() instead, eg:

std::erase_if(possible, [](const auto& item) { return item.second == 1; });
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