DoubleStream reduce(double identity, DoubleBinaryOperator op) in Java with Examples

DoubleStream reduce(double identity, DoubleBinaryOperator op) performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value.

A reduction operation or fold takes a sequence of input elements and combines them into a single summary result, such as finding the sum or maximum of a set of numbers. An operator or function op is associative if the following holds :

(a op b) op c == a op (b op c)

This is a terminal operation i.e, it may traverse the stream to produce a result or a side-effect. After the terminal operation is performed, the stream pipeline is considered consumed, and can no longer be used.



Syntax :

double reduce(double identity,  DoubleBinaryOperator op)

Parameters :

  • identity : The identity value for the accumulating function.
  • DoubleBinaryOperator : An operation upon two double-valued operands and producing a double-valued result.
  • op : An associative, stateless function for combining two values.

Return Value : The result of the reduction.

Example 1 :

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// Java code for DoubleStream reduce
// (double identity, DoubleBinaryOperator op)
import java.util.*;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating a DoubleStream
        DoubleStream stream = DoubleStream.of(1.2, 2.3,
                                              3.4, 4.5, 5.6);
  
        // Using DoubleStream reduce
        // (double identity, DoubleBinaryOperator op)
        double answer = stream.reduce(5, (num1, num2)
                                             -> (num1 + num2));
  
        // Displaying the result
        System.out.println(answer);
    }
}

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Output :

22.0

Example 2 :

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// Java code for DoubleStream reduce
// (double identity, DoubleBinaryOperator op)
import java.util.*;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating a DoubleStream
        DoubleStream stream = DoubleStream.of(2.1, 3.2,
                                              4.3, 5.4, 6.5);
  
        // Using DoubleStream reduce
        // (double identity, DoubleBinaryOperator op)
        double answer = stream.reduce(3, (num1, num2)
                                             -> (num1 * num2) * 2);
  
        // Displaying the result
        System.out.println(answer);
    }
}

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Output :

97367.96160000002


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