Java Lambda Expression - Aggregation

A lambda expression is an anonymous function which performs arithmetic or relational operation over an array of data in sequential or parallel manner. It replaces for-loop like operation over array objects.

lambda expression

Stream Object The array of data might be a java primitive data type (integer or long or double) or a java collection object (ArrayList). In order to execute the lambda expression over array of data, we need a Stream object (IntStream, LongStream or DoubleStream).

The Stream object can be obtained by many ways, however, an example shown here.

   An array variable X initialized with random integers 
      int X [] = { 48, 21, 23, 45, 53, 
                   14, 18, 34, 11, 
                   19,21,23,53
                 };

 IntStream object is obtained by passing X as a argument 
                to Arrays.stream function.
      IntStream intstream =Arrays.stream(X)


An array variable X2 initialized with random integers 

      double X2 [] = { 0.58, 2.1, 1.23, 0.45, 3.57, 
                       5.62, 0.86, 0.234, 0.361, 
                       0.296,0.211
                      };


DoubleStream object is obtained by passing X2 as a argument 
                 to Arrays.stream function.

      DoubleStream dblstream =Arrays.stream(X2)

    The obtaining Stream object depends on 
        type of argument passed over Arrays.stream.

The Stream object's member functions support the following application over array of data using lambda functions, They are,

• Aggregation
• Filtering
• Maping
• For Each

Lambda expression Aggregation over array of interger

The following Java code shown below is example of lambda expression application over on array of integers, generated randomly using the Random object. The lambda aggregation functions like

        sum  -  sum over an array elements, 

        average  -  average over an array of elements  

        min    - find a element have minimum value 
                          in the array of elements
        max    - find a element have maximum value 
                          in the array of elements

   

it results one element output given over array of elements

import java.util.Arrays;
import java.util.Random;
import java.util.stream.IntStream;

public class Lambda1 {

 public static void main(String[] args) 
 {     
  int size=20;
  int X [] = new int[size];  
  Random rd = new Random();  
  for (int n=0;n<size;n++)
   X[n] = rd.nextInt(100);
        
    
    System.out.println("\n A randomly integer array ");
    System.out.println(Arrays.toString(X));
    
    System.out.println("\n Find sum of the array ");
    IntStream ints=Arrays.stream(X);
    int sum = ints.sum();    
    System.out.println("sum  :"+ sum);
    
    System.out.println("\n Find  Average of the array ");
    IntStream ints2=Arrays.stream(X);
    double average = ints2.average().getAsDouble();            
    System.out.println("Average  :"+ average);
    
    
    System.out.println("\nFind Maximum of the array ");
    IntStream ints3=Arrays.stream(X);
    int max = ints3.max().getAsInt();
    
    System.out.println("Max  :"+ max);

    System.out.println("\nFind Minimum of the array ");
    IntStream ints4=Arrays.stream(X);
    int min = ints4.min().getAsInt();    
    System.out.println("Min :"+ min);

               
 
 }

}

Output

 A randomly integer array 

[33, 87, 30, 62, 47, 46, 93, 12, 37, 24, 38,
        67, 15, 94, 39, 21, 89, 35, 83, 48]

 Find sum of the array 
sum  :1000

 Find  Average of the array 
Average  :50.0

Find Maximum of the array 
Max  :94

Find Minimum of the array 
Min :12