Sort vector by column

• 2D 벡터를 정렬할때 첫번째 원소를 기준으로 정렬하는게 아닌 n번째 원소(열)를 기준으로 정렬이 필요할 때가 있다.
• 아래의 코드와 같이 할 수 있다.

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

using namespace std;

void print2DVector(vector<vector<int>> &v) {
    for(const auto &row: v) {
        for(const auto &r: row) {
            cout<<r<<" ";
        } cout<<endl;
    } cout<<endl;
}

int main() {

    vector<vector<int>> v = {{4,3,5,3}, 
                     {2,6,3,7}, 
                     {6,8,5,1}, 
                     {5,6,1,5}};
    
    cout<<"Before sort by column: "<<endl;
    print2DVector(v);

    sort(v.begin(), v.end(), [](vector<int> &v1, vector<int> &v2) {return v1[3]<v2[3];});
    cout<<"After sort by last column: "<<endl;
    print2DVector(v);

    sort(v.begin(), v.end(), [](vector<int> &v1, vector<int> &v2) {return v1[2]<v2[2];});
    cout<<"After sort by second column from the back: "<<endl;
    print2DVector(v);

    return 0;
}

Github

• https://github.com/kon6443/Algorithms/blob/main/Algorithm/Sort_2D_vector_by_column/main.cpp

References

• https://stackoverflow.com/questions/45494567/c-how-to-sort-the-rows-of-a-2d-vector-by-the-values-in-each-rows-column