[ACCEPTED]-Extract every other element of a vector-stdvector

Accepted answer

Score: 18

I am unsure what is meant by better but if C++11 1 you could use std::partition_copy:

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main()
{
    std::vector<int> v1;
    for (int i = 0; i < 100; i++) v1.push_back(i);

    std::vector<int> v2;
    std::vector<int> v3;

    bool toggle = false;
    std::partition_copy(v1.begin(),
                        v1.end(),
                        std::back_inserter(v2),
                        std::back_inserter(v3),
                        [&toggle](int) { return toggle = !toggle; });

    std::cout << v2.size() << "\n";
    std::cout << v3.size() << "\n";

    return 0;
}

See online demo http://ideone.com/pa9rW .

Score: 6

// Make sure the vector is not empty
if(!v.empty()){
    for(size_t i = 0; i < (v.size() - 1); i+=2){
        v1.push_back(v[i]);
        v2.push_back(v[i + 1]);
    }

    if(v.size() % 2) v1.push_back(v.back());
}

As noted in the comments by multiple people 4 you have to check that the vector is not 3 empty. You could avoid the push back calls 2 by resizing both vectors prior to the loop 1 ie.

// Make sure the vector is not empty
if(!v.empty()){
    v1.resize((v.size() + 1) / 2);
    v2.resize(v.size() / 2);
    for(size_t i = 0, j = 0; i < (v.size() - 1); i+=2, j++){
        v1[j] = (v[i]);
        v2[j] = (v[i + 1]);
    }

    if(v.size() % 2) v1.push_back(v.back());
}

Source: stackoverflow.com

Initialize std::array with a range (pair of iterators)

Pretty-print a std::vector in C++

Why doesn't this use of emplace_back with deleted copy constructor work?

vector<char> VS vector<bool> in C++11

Is there a more efficient way to set a std::vector from a stream?

Why doesn't vector::clear remove elements from a vector?

Fastest way to negate a std::vector

Is it safe to swap two different vectors in C++, using the std::vector::swap method?

Overhead to using std::vector?

std::dynarray vs std::vector

Cookie Warning

We use cookies to improve the performance of the site. By staying on our site, you agree to the terms of use of cookies.