CODEWITHSUNDEEP
c++arraysvector
k-a-v
k-a-v

Reputation: 347

Convert vector of arrays into vector of vectors c++

I need a way to convert data in the form of std::vector<std::array<int, 2> > into std::vector<std::vector<int> > quickly. I have the following solution, but on large vectors this is quite slow for me. 

std::vector<std::array<int, 2> > data; // filled with data
std::vector<std::vector<int> > mod;

for (int i = 0; i < data.size(); i++) {
   mod.push_back(vector<int>(data[i].begin(), data[i].end()));
}

Is there a more efficient way to do it?

Upvotes: 0

Views: 492

Answers (1)

john
john

Reputation: 88017

The following should be more efficient

std::vector<std::array<int, 2> > data; // filled with data
std::vector<std::vector<int> > mod;

mod.reserve(data.size());
for (int i = 0; i < data.size(); i++) {
   mod.emplace_back(data[i].begin(), data[i].end());
}

reserve prevents reallocation of the mod vector as it grows, and emplace_back constructs the smaller vectors in place, potentially avoiding some copying of data.

Upvotes: 2

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