Sort 2d Array In Java

Sort 2d Array In Java | In this section, we will be explaining how to sort 2d arrays by using sorting techniques and functions available in the Java library. 

2d Array Sorting In Java

Let us see 2d Array Sorting In Java using loops.

public class Main {

   // sort 2D array in descending order
   public static void sort2dArray(int arr[][]) {
      int n = arr.length;
      for (int i = 0; i < n; i++) {
         for (int j = 0; j < n; j++) {
            for (int k = 0; k < n; k++) {
               for (int l = 0; l < n; l++) {
                  if (arr[i][j] > arr[k][l]) {
                     // swap
                     int temp = arr[i][j];
                     arr[i][j] = arr[k][l];
                     arr[k][l] = temp;
                  }
               }
            }
         }
      }
   }

   public static void display2dArray(int arr[][]) {
      for (int i = 0; i < arr.length; i++) {
         for (int j = 0; j < arr[i].length; j++) {
            System.out.print(arr[i][j] + " ");
         }
         System.out.println();
      }
   }

   public static void main(String args[]) {
      int array[][] = 
              {
                { 10, 28, 72, 91 }, 
                { 27, 33, 40, 52 }, 
                { 69, 75, 73, 72 }, 
                { 46, 33, 31, 2 } 
              };

      System.out.println("2d Array: ");
      display2dArray(array);

      // sort the array
      sort2dArray(array);

      System.out.println("\nSorted 2d Array: ");
      display2dArray(array);
   }
}

Output:-

2d Array:
10 28 72 91
27 33 40 52
69 75 73 72
46 33 31 2

Sorted 2d Array:
91 75 73 72
72 69 52 46
40 33 33 31
28 27 10 2

In the above program the same original array is sorted. If you want to get a separate array (without changing the original array) then before sorting create a copy of 2D array and return the resultant array. We have discussed here in detail how to copy a 2D array in Java?

In the above example we have sorted array in descending order. But if you want to sort array in ascending order then you can use the below method instead.

// sort 2D array in ascending order
public static void sort2dArray(int arr[][]) {
   int n = arr.length;
   for (int i = 0; i < n; i++) {
      for (int j = 0; j < n; j++) {
         for (int k = 0; k < n; k++) {
            for (int l = 0; l < n; l++) {
               if (arr[i][j] < arr[k][l]) {
                  // swap
                  int temp = arr[i][j];
                  arr[i][j] = arr[k][l];
                  arr[k][l] = temp;
               }
            }
         }
      }
   }
}

Output:-

2d Array:
10 28 72 91
27 33 40 52
69 75 73 72
46 33 31 2

Sorted 2d Array:
2 10 27 28
31 33 33 40
46 52 69 72
72 73 75 91

Sort 2d Array in Java Row Wise

In the above example we have sorted an entire 2d array. But sometimes we may need to sort them row wise. It means, in a particular row elements will be sorted in ascending or descending order.

// sort 2D array row wise in ascending order
public static void sort2dArrayRowWise(int arr[][]) {
   for (int i = 0; i < arr.length; i++) {
      for (int j = 0; j < arr[i].length; j++) {
         for (int k = 0; k < arr[i].length - j - 1; k++) {
            if (arr[i][k] > arr[i][k + 1]) {
               // swap
               int temp = arr[i][k];
               arr[i][k] = arr[i][k + 1];
               arr[i][k + 1] = temp;
            }
         }
      }
   }
}

Output:-

2d Array:
10 28 72 91
27 33 40 52
69 75 73 72
46 33 31 2

Sorted 2d Array:
10 28 72 91
27 33 40 52
69 72 73 75
2 31 33 46

To sort 2d array in Java row wise descending order change the if condition of the above method.

if (arr[i][k] < arr[i][k + 1]) {
   // swap
   int temp = arr[i][k];
   arr[i][k] = arr[i][k + 1];
   arr[i][k + 1] = temp;
}

Sort a 2d Array in Java Using sort() Method

In the Java Arrays class, a separate method is given to sort the one-dimesional array:- Arrays.sort() method. The Arrays.sort() method uses Dual-Pivot Quicksort technique to sort the array. We can take the help of Arrays.sort() method to sort a 2d array row wise.

2d array sorting in Java Row Wise using sort() Method

import java.util.Arrays;

public class Main {

   public static void display2dArray(int arr[][]) {
      for (int i = 0; i < arr.length; i++) {
         for (int j = 0; j < arr[i].length; j++) {
            System.out.print(arr[i][j] + " ");
         }
         System.out.println();
      }
   }

   public static void main(String args[]) {
      int array[][] = 
              { 
                { 10, 28, 72, 91 }, 
                { 27, 33, 40, 52 }, 
                { 69, 75, 73, 72 }, 
                { 46, 33, 31, 2 } 
              };

      System.out.println("2d Array: ");
      display2dArray(array);

      // sort the array
      for (int i = 0; i < array.length; i++) {
         Arrays.sort(array[i]);
      }

      System.out.println("\nSorted 2d Array: ");
      display2dArray(array);
   }
}

Output:

2d Array:
10 28 72 91
27 33 40 52
69 75 73 72
46 33 31 2

Sorted 2d Array:
10 28 72 91
27 33 40 52
69 72 73 75
2 31 33 46

Java How To Sort A String 2d Array

We have seen several examples for sorting of integer 2d array. Now, let us see an example of sorting of string 2d array.

2d Array Sorting in Java Row Wise

import java.util.Arrays;

public class Main {

   public static void display2dArray(String arr[][]) {
      for (int i = 0; i < arr.length; i++) {
         for (int j = 0; j < arr[i].length; j++) {
            System.out.print(arr[i][j] + " ");
         }
         System.out.println();
      }
   }

   public static void main(String args[]) {
      String array[][] = 
           { 
              { "Stiphen", "John" }, 
              { "Henry", "Adam" }, 
              { "Potter", "Harry" } 
           };
      System.out.println("2d Array: ");
      display2dArray(array);

      // sort the array
      for (int i = 0; i < array.length; i++) {
         Arrays.sort(array[i]);
      }

      System.out.println("\nSorted 2d Array: ");
      display2dArray(array);
   }
}

Output:

2d Array:
Stiphen John
Henry Adam
Potter Harry

Sorted 2d Array:
John Stiphen
Adam Henry
Harry Potter

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