How to copy vector column-wise?

Question

I've a 2d vector say

vector < vector < int > > sample;

sample = 1 2 3 4 5
         6 7 8 9 0
         1 1 1 1 1
         2 2 2 2 2

Now I want to copy only the last two columns into another 2d vector like

vector < vector < int > > test;

test = 4 5
       9 0 
       1 1
       2 2

How can I do this efficiently ?

Answer 1

Maybe like this?

#include <algorithm>

vector<vector<int> > new_vector;
new_vector.resize(sample.size());

for (size_t i = 0; i < new_vector.size(); ++i) {
    new_vector[i].resize(2);
    copy(sample[i].end() - 2, sample[i].end(), new_vector[i].begin());
}