1. Operators
  2. Mathematical and Aggregate
  3. Sum

Sum

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

The Sum operator operates on an Observable that emits numbers (or items that can be evaluated as numbers), and emits a single value: the sum of all of the numbers emitted by the source Observable.

See Also

Language-Specific Information:

TBD

TBD

In RxGroovy, this operator is not in the ReactiveX core, but is part of the distinct rxjava-math module, where it is implemented with four type-specific operators: sumDouble, sumFloat, sumInteger, and sumLong. The following example shows how these operators work:

Sample Code

def myObservable = Observable.create({ aSubscriber ->
  if(false == aSubscriber.isUnsubscribed()) aSubscriber.onNext(4);
  if(false == aSubscriber.isUnsubscribed()) aSubscriber.onNext(3);
  if(false == aSubscriber.isUnsubscribed()) aSubscriber.onNext(2);
  if(false == aSubscriber.isUnsubscribed()) aSubscriber.onNext(1);
  if(false == aSubscriber.isUnsubscribed()) aSubscriber.onCompleted();
});

Observable.sumInteger(myObservable).subscribe(
  { println(it); },                  // onNext
  { println("Error encountered"); }, // onError
  { println("Sequence complete"); }  // onCompleted
);
10
Sequence complete
sum

You can also sum not the items themselves but the results of a function applied to each item, as in the illustration above, which emits the sum of the number of sides on the figures emitted by the source Observable.

stringConcat

In the distinct StringObservable class (not part of RxGroovy by default) there is also a stringConcat operator that converts an Observable that emits a sequence of strings into an Observable that emits a single string that represents the concatenation of them all.

join

In the distinct StringObservable class (not part of RxGroovy by default) there is also a join operator that converts an Observable that emits a sequence of strings into an Observable that emits a single string that represents the concatenation of each of them, delimited by a string of your choosing.

This operator is not in the RxJava core, but is part of the distinct rxjava-math module, where it is implemented with four type-specific operators: sumDouble, sumFloat, sumInteger, and sumLong.

sum

You can also sum not the items themselves but the results of a function applied to each item, as in the illustration above, which emits the sum of the number of sides on the figures emitted by the source Observable.

stringConcat

In the distinct StringObservable class (not part of RxJava by default) there is also a stringConcat operator that converts an Observable that emits a sequence of strings into an Observable that emits a single string that represents the concatenation of them all.

join

In the distinct StringObservable class (not part of RxJava by default) there is also a join operator that converts an Observable that emits a sequence of strings into an Observable that emits a single string that represents the concatenation of each of them, delimited by a string of your choosing.

sum

RxJS implements this operator as sum. The following code sample shows how to use it:

Sample Code

var source = Rx.Observable.range(0, 9).sum();

var subscription = source.subscribe(
    function (x) {
        console.log('Next: ' + x);
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });
Next: 45
Completed
sum

You can also sum not the items themselves but the results of a function applied to each item, as in the illustration above, which emits the sum number of sides on the figures emitted by the source Observable.

Sample Code

var arr = [
    { value: 1 },
    { value: 2 },
    { value: 3 }
];

var source = Rx.Observable.fromArray(arr).sum(function (x) {
    return x.value;
});

var subscription = source.subscribe(
    function (x) {
        console.log('Next: ' + x);
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });
Next: 6
Completed

sum is found in the following distributions:

  • rx.all.js
  • rx.all.compat.js
  • rx.aggregates.js

It requires one of the following:

  • rx.js
  • rx.compat.js
  • rx.lite.js
  • rx.lite.compat.js

TBD

TBD

RxPHP implements this operator as sum.

Computes the sum of a sequence of values

Sample Code

//from https://github.com/ReactiveX/RxPHP/blob/master/demo/sum/sum.php

$source = Rx\Observable::range(1, 10)
    ->sum();

$subscription = $source->subscribe($stdoutObserver);

   
Next value: 55
Complete!

TBD

TBD

TBD