CODE EXAMPLE FOR CPP

sort a 2d vector c++ stl

// C++ code to demonstrate sorting of a
// 2D vector on basis of a column
#include <algorithm> // for sort()
#include <iostream>
#include <vector> // for 2D vector
using namespace std;
 
// Driver function to sort the 2D vector
// on basis of a particular column
bool sortcol(const vector<int>& v1, const vector<int>& v2)
{
    return v1[1] < v2[1];
}
 
// Driver Code
int main()
{
    // Initializing 2D vector "vect" with
    // values
    vector<vector<int> > vect{ { 3, 5, 1 },
                               { 4, 8, 6 },
                               { 7, 2, 9 } };
 
    // Number of rows;
    int m = vect.size();
 
    // Number of columns (Assuming all rows
    // are of same size). We can have different
    // sizes though (like Java).
    int n = vect[0].size();
 
    // Displaying the 2D vector before sorting
    cout << "The Matrix before sorting is:
";
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++)
            cout << vect[i][j] << " ";
        cout << endl;
    }
 
    // Use of "sort()" for sorting on basis
    // of 2nd column
    sort(vect.begin(), vect.end(), sortcol);
 
    // Displaying the 2D vector after sorting
    cout << "The Matrix after sorting is:
";
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++)
            cout << vect[i][j] << " ";
        cout << endl;
    }
    return 0;
}