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

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We are given a 2D array of order N X M and a column number K ( 1<=K<=m). Our task is to sort the 2D array according to values in Column K.

Examples:

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

Java Program to Sort a 2D Array according to values in any given Column

Java
// Java Program to Sorting a 2D Array according to values
// in any given column 
import java.io.*;
import java.util.*;

// Class
class GFG {
  
    // Method to sort by column
    public static void sortbyColumn(int arr[][], int col)
    {
        // Using built-in sort function Arrays.sort with lambda expressions
      
      Arrays.sort(arr, (a, b) -> Integer.compare(a[col],b[col])); // increasing order
        
    }
    public static void main(String args[])
    {
        int matrix[][] = { { 39, 27, 11, 42 },
                           { 10, 93, 91, 90 },
                           { 54, 78, 56, 89 },
                           { 24, 64, 20, 65 } };
        // Sort this matrix by 3rd Column
        int col = 3;
        sortbyColumn(matrix, col - 1);
  
        // Display the sorted Matrix
        for (int i = 0; i < matrix.length; i++) {
          
            for (int j = 0; j < matrix[i].length; j++)
                System.out.print(matrix[i][j] + " ");
            System.out.println();
            
        }
    }
}

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

Java Program to sort 2D Matrix according to any Column

The idea is to use Arrays.sort in Java.

Syntax:

Arrays.sort(arr, (a,b)->a[0]-b[0]);
Java
// Java Code to sort 2D Matrix
// according to any Column

// Importing required classes
import java.util.*;
class sort2DMatrixbycolumn {

    // Function to sort by column
    public static void sortbyColumn(int arr[][], int col)
    {
        // Using built-in sort function Arrays.sort
        Arrays.sort(arr, new Comparator<int[]>() {
            @Override
            // Compare values according to columns
            public int compare(final int[] entry1,
                               final int[] entry2)
            {

                // To sort in descending order revert
                // the '>' Operator
                if (entry1[col] > entry2[col])
                    return 1;
                else
                    return -1;
            }
        }); // End of function call sort().
    }

    // Main driver method
    public static void main(String args[])
    {
        int matrix[][] = { { 39, 27, 11, 42 },
                           { 10, 93, 91, 90 },
                           { 54, 78, 56, 89 },
                           { 24, 64, 20, 65 } };

        // Sorting the matrix by 3rd Column
        int col = 3;
        sortbyColumn(matrix, col - 1);

        // Printing the sorted matrix
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[i].length; j++)
                System.out.print(matrix[i][j] + " ");
            System.out.println();
        }
    }
}

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


Explanation of the above Program:

  • If element at 0 index of array a is greater than element at 0 index of array b, their difference will be positive. This means array a is kept after array b.
  • If element at 0 index of array a is smaller than element at 0 index of array b, their difference will be negative. This means array b is kept after array a.
  • If both the elements are equal, then their difference will be 0. This means that they will be equally placed.
  • On the basis of these values, the entire array is sorted.

Time complexity: O(n log n) where n is the number of rows.



Last Updated : 21 Mar, 2024
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