CODEWITHSUNDEEP
c++c++11vectorstlcopy
nalyd88
nalyd88

Reputation: 5138

Efficiently moving contents of std::unordered_set to std::vector

In my code I have a std::unordered_set and I need to move the data into a std::vector. I'm using the std::unordered_set while getting the data to ensure only unique values are stored prior to converting to a std::vector. My question is how do I move the contents to the std::vector the most efficiently? I don't need the std::unordered_set after the data is moved. I currently have the following:

std::copy(set.begin(), set.end(), std::back_inserter(vector));

Upvotes: 24

Views: 38082

Answers (2)

Vinicius Alves
Vinicius Alves

Reputation: 1

I'm using C++ 17 and this approach worked fine for me:

vector<string> vec(set.begin(), set.end());

Please reference to Convert Set To Vector in C++ to more examples.

Upvotes: 0

Barry
Barry

Reputation: 303087

Before C++17, the best you can do is:

vector.insert(vector.end(), set.begin(), set.end());

The set's elements are const, so you can't move from them - moving is just copying.

After C++17, we get extract():

vector.reserve(set.size());
for (auto it = set.begin(); it != set.end(); ) {
    vector.push_back(std::move(set.extract(it++).value()));
}

Although given your comment that your data is doubles, this wouldn't matter.

Upvotes: 39

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