Sorting a 2D Array according to values in any given column in Java

A 2D array can be sorted based on the values of any selected column. Java provides Arrays.sort() with a comparator, which allows us to compare rows using the value at the required column.

Illustration:

Input: If our 2D array is given as (Order 4X4)
39 27 11 42
10 93 91 90
54 78 56 89
24 64 20 65

Sorting it by values in column 3

Output:

39 27 11 42
24 64 20 65
54 78 56 89
10 93 91 90

Approach

• Select the column according to which the rows should be sorted.
• Use Arrays.sort() with a comparator.
• Compare the values of the selected column in each row.
• The complete rows are rearranged based on those values.

import java.io.*;
import java.util.*;

class GFG {
    public static void sortbyColumn(int a[][], int c){      
      Arrays.sort(a, (x, y) -> Integer.compare(x[c],y[c]));  
    }
  
    public static void main(String args[])
    {
        int m[][] = { { 39, 27, 11, 42 },
                     { 10, 93, 91, 90 },
                     { 54, 78, 56, 89 },
                     { 24, 64, 20, 65 } };
       
      	// Sort this matrix by 3rd Column
      	int c = 3;
      
        sortbyColumn(m, c - 1);
  
        // Display the sorted Matrix
        for (int i = 0; i < m.length; i++) {
          
            for (int j = 0; j < m[i].length; j++)
                System.out.print(m[i][j] + " ");
          
            System.out.println();
            
        }
    }
}

39 27 11 42 
24 64 20 65 
54 78 56 89 
10 93 91 90 

Explanation

• column = 2 represents the 3rd column because array indexing starts from 0.
• a[column] and b[column] are compared for two rows.
• Integer.compare() sorts the rows in ascending order.
• The entire row moves together; only the sorting order changes.