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
• min( ) — emits the minimum value emitted by a source Observable
• minBy( ) — emits the item emitted by the source Observable that has the minimum key value
• max( ) — emits the maximum value emitted by a source Observable
• maxBy( ) — emits the item emitted by the source Observable that has the maximum key value

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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(
  { println(it); },                  // onNext
  { println("Error encountered"); }, // onError
  { println("Sequence complete"); }  // onCompleted
);

3
Sequence complete

see also:

• RxJS: count
• Linq: Count
• Introduction to Rx: Count

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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(
  { println(it); },                  // onNext
  { println("Error encountered"); }, // onError
  { println("Sequence complete"); }  // onCompleted
);

10
Sequence complete

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

see also:

• RxJS: sum
• Linq: Sum
• Introduction to Rx: Min, Max, Sum, and Average

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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(
  { println(it); },                  // onNext
  { println("Error encountered"); }, // onError
  { println("Sequence complete"); }  // onCompleted
);

2
Sequence complete

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

Note that these methods will fail with an IllegalArgumentException if the source Observable does not emit any items.

see also:

• RxJS: average
• Linq: Average
• Introduction to Rx: Min, Max, Sum, and Average

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min( )

emits the minimum value emitted by a source Observable

see also:

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minBy( )

emits the item emitted by the source Observable that has the minimum key value

see also:

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max( )

emits the maximum value emitted by a source Observable

see also:

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maxBy( )

emits the item emitted by the source Observable that has the maximum key value

see also: