ElementAt

emit only item n emitted by an Observable
Open interactive diagram on rxmarbles.com

The ElementAt operator pulls an item located at a specified index location in the sequence of items emitted by the source Observable and emits that item as its own sole emission.

See Also

Language-Specific Information

elementAt

RxGroovy implements this operator as elementAt. Pass elementAt a zero-based index value and it will emit the solitary item from the source Observable’s sequence that matches that index value (for example, if you pass the index value 5, elementAt will emit the sixth item emitted by the source Observable).

If you pass in a negative index value, or if the source Observable emits fewer than index value + 1 items, elementAt will throw an IndexOutOfBoundsException.

elementAtOrDefault

RxGroovy also implements the elementAtOrDefault operator. It differs from elementAt in that it will not throw an exception if the source Observable emits fewer than index value + 1 items. Instead, it will emit a “default” item that you specify with an additional parameter to elementAtOrDefault.

If you pass in a negative index value, elementAt will throw an IndexOutOfBoundsException.

elementAt and elementAtOrDefault do not by default operate on any particular Scheduler.

elementAt

RxGroovy implements this operator as elementAt. Pass elementAt a zero-based index value and it will emit the solitary item from the source Observable’s sequence that matches that index value (for example, if you pass the index value 5, elementAt will emit the sixth item emitted by the source Observable).

If you pass in a negative index value, or if the source Observable emits fewer than index value + 1 items, elementAt will throw an IndexOutOfBoundsException.

elementAtOrDefault

RxGroovy also implements the elementAtOrDefault operator. It differs from elementAt in that it will not throw an exception if the source Observable emits fewer than index value + 1 items. Instead, it will emit a “default” item that you specify with an additional parameter to elementAtOrDefault.

If you pass in a negative index value, elementAt will throw an IndexOutOfBoundsException.

elementAt and elementAtOrDefault do not by default operate on any particular Scheduler.

elementAt

RxJS implements this operator as elementAt. Pass elementAt a zero-based index value and it will emit the solitary item from the source Observable’s sequence that matches that index value (for example, if you pass the index value 5, elementAt will emit the sixth item emitted by the source Observable).

If there is no element in the source sequence with the index value you specify, elementAt will issue an onError notification: “Argument out of range”

Sample Code

var source = Rx.Observable.fromArray([1,2,3,4])
    .elementAt(1);

var subscription = source.subscribe(
    function (x) { console.log('Next: ' + x); },
    function (err) { console.log('Error: ' + err); },
    function () { console.log('Completed'); });
Next: 2
Completed

You may optionally pass in a default value that elementAt will emit if the source Observable emits no values:

Sample Code

var source = Rx.Observable.fromArray([])
    .element({defaultValue: 23});

var subscription = source.subscribe(
    function (x) { console.log('Next: ' + x); },
    function (err) { console.log('Error: ' + err); },
    function () { console.log('Completed'); });
Next: 23
Completed

elementAt is found in each of the following distributions:

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

They require one of the following distributions:

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

© ReactiveX contributors
Licensed under the Apache License 2.0.
http://reactivex.io/documentation/operators/elementat