Mathematical Operators

This section explains operators that perform mathematical operations on the items emitted by Observables.

• count( ) — counts the number of items emitted by an Observable and emits this count
• sum( ) — adds the Integers emitted by an Observable and emits this sum
• sumLongs( ) — adds the Longs emitted by an Observable and emits this sum
• sumFloats( ) — adds the Floats emitted by an Observable and emits this sum
• sumDoubles( ) — adds the Floats emitted by an Observable and emits this sum
• average( ) — calculates the average of Integers emitted by an Observable and emits this average
• averageLongs( ) — calculates the average of Longs emitted by an Observable and emits this average
• averageFloats( ) — calculates the average of Floats emitted by an Observable and emits this average
• averageDoubles( ) — calculates the average of Doubles emitted by an Observable and emits this average

count( )

counts the number of items emitted by an Observable and emits this count

The count( ) method returns an Observable that emits a single item: an Integer that represents the total number of items emitted by the source Observable, as shown in the following sample code:

def myObservable = Observable.create({ anObserver ->
  anObserver.onNext('Three');
  anObserver.onNext('Two');
  anObserver.onNext('One');
  anObserver.onCompleted();
});

myObservable.count().subscribe(
  [ onNext:{ myWriter.println(it); },
    onCompleted:{ myWriter.println("Sequence complete"); },
    onError:{ myWriter.println("Error encountered"); } ]
);

3
Sequence complete

sum( )

adds the numbers emitted by an Observable and emits this sum

The sum( ) method returns an Observable that adds the Integers emitted by a source Observable and then emits this sum as an Integer, as shown in the following sample code:

def myObservable = Observable.create({ anObserver ->
  anObserver.onNext(4);
  anObserver.onNext(3);
  anObserver.onNext(2);
  anObserver.onNext(1);
  anObserver.onCompleted();
});

myObservable.sum().subscribe(
  [ onNext:{ myWriter.println(it); },
    onCompleted:{ myWriter.println("Sequence complete"); },
    onError:{ myWriter.println("Error encountered"); } ]
);

10
Sequence complete

There are also specialized "sum" methods for Longs, Floats, and Doubles (sumLongs( ), sumFloats( ), and sumDoubles( )).

average( )

calculates the average of numbers emitted by an Observable and emits this average

The average( ) method returns an Observable that calculates the average of the Integers emitted by a source Observable and then emits this average as an Integer, as shown in the following sample code:

def myObservable = Observable.create({ anObserver ->
  anObserver.onNext(4);
  anObserver.onNext(3);
  anObserver.onNext(2);
  anObserver.onNext(1);
  anObserver.onCompleted();
});

myObservable.average().subscribe(
  [ onNext:{ myWriter.println(it); },
    onCompleted:{ myWriter.println("Sequence complete"); },
    onError:{ myWriter.println("Error encountered"); } ]
);

2
Sequence complete

There are also specialized "average" methods for Longs, Floats, and Doubles (averageLongs( ), averageFloats( ), and averageDoubles( )).