将 arrays 的向量转换为向量的向量 c++

Question

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?

Answer 1

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.