1. Operators
  2. Conditional and Boolean
  3. SkipWhile

SkipWhile

discard items emitted by an Observable until a specified condition becomes false

SkipWhile

The SkipWhile subscribes to the source Observable, but ignores its emissions until such time as some condition you specify becomes false, at which point SkipWhile begins to mirror the source Observable.

See Also

Language-Specific Information:

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skipWhile

The skipWhile operator returns an Observable that discards items emitted by the source Observable until such time as a function, applied to an item emitted by that Observable, returns false, whereupon the new Observable emits that item and the remainder of the items emitted by the source Observable. 

numbers = Observable.from( [1, 2, 3, 4, 5, 6, 7, 8, 9] );

numbers.skipWhile({ (5 != it) }).subscribe(
  { println(it); },                          // onNext
  { println("Error: " + it.getMessage()); }, // onError
  { println("Sequence complete"); }          // onCompleted
);
5
6
7
8
9
Sequence complete

skipWhile does not by default operate on any particular Scheduler.

skipWhile

The skipWhile operator returns an Observable that discards items emitted by the source Observable until such time as a function, applied to an item emitted by that Observable, returns false, whereupon the new Observable emits that item and the remainder of the items emitted by the source Observable.

skipWhile does not by default operate on any particular Scheduler.

skipWhile

RxJS implements the skipWhile operator. You pass it a function that governs the skipping process. skipWhile calls that function for each item emitted by the source Observable until such time as the function returns false, whereupon skipWhile begins mirroring the source Observable (starting with that item). The function takes three parameters:

  1. the emitted item
  2. the zero-based index of that item in the sequence of emissions
  3. the source Observable

You may optionally pass a second parameter to skipWhile. If so, that item will also be available to your predicate function as “this”.

Sample Code

var source = Rx.Observable.range(1, 5)
    .skipWhile(function (x) { return x < 3; });

var subscription = source.subscribe(
    function (x) { console.log('Next: ' + x); },
    function (err) { console.log('Error: ' + err); },
    function () { console.log('Completed'); });
Next: 3
Next: 4
Next: 5
Completed

skipWhile is found in each of the following distributions:

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

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RxPHP implements this operator as skipWhile.

Bypasses elements in an observable sequence as long as a specified condition is true and then returns the remaining elements.

Sample Code

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

$observable = Rx\Observable::range(1, 5)
    ->skipWhile(function ($x) {
        return $x < 3;
    });

$observable->subscribe($stdoutObserver);

   
Next value: 3
Next value: 4
Next value: 5
Complete!

RxPHP also has an operator skipWhileWithIndex.

Bypasses elements in an observable sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function.

Sample Code

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

$observable = Rx\Observable::range(1, 5)
    ->skipWhileWithIndex(function ($i, $value) {
        return $i < 3;
    });

$observable->subscribe($stdoutObserver);

   
Next value: 4
Next value: 5
Complete!

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