[6a3a178] | 1 | import { OperatorFunction } from '../types';
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| 2 | /**
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| 3 | * Groups pairs of consecutive emissions together and emits them as an array of
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| 4 | * two values.
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| 5 | *
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| 6 | * <span class="informal">Puts the current value and previous value together as
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| 7 | * an array, and emits that.</span>
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| 8 | *
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| 9 | * ![](pairwise.png)
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| 10 | *
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| 11 | * The Nth emission from the source Observable will cause the output Observable
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| 12 | * to emit an array [(N-1)th, Nth] of the previous and the current value, as a
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| 13 | * pair. For this reason, `pairwise` emits on the second and subsequent
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| 14 | * emissions from the source Observable, but not on the first emission, because
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| 15 | * there is no previous value in that case.
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| 16 | *
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| 17 | * ## Example
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| 18 | * On every click (starting from the second), emit the relative distance to the previous click
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| 19 | * ```ts
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| 20 | * import { fromEvent } from 'rxjs';
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| 21 | * import { pairwise, map } from 'rxjs/operators';
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| 22 | *
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| 23 | * const clicks = fromEvent(document, 'click');
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| 24 | * const pairs = clicks.pipe(pairwise());
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| 25 | * const distance = pairs.pipe(
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| 26 | * map(pair => {
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| 27 | * const x0 = pair[0].clientX;
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| 28 | * const y0 = pair[0].clientY;
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| 29 | * const x1 = pair[1].clientX;
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| 30 | * const y1 = pair[1].clientY;
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| 31 | * return Math.sqrt(Math.pow(x0 - x1, 2) + Math.pow(y0 - y1, 2));
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| 32 | * }),
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| 33 | * );
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| 34 | * distance.subscribe(x => console.log(x));
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| 35 | * ```
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| 36 | *
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| 37 | * @see {@link buffer}
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| 38 | * @see {@link bufferCount}
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| 39 | *
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| 40 | * @return {Observable<Array<T>>} An Observable of pairs (as arrays) of
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| 41 | * consecutive values from the source Observable.
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| 42 | * @method pairwise
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| 43 | * @owner Observable
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| 44 | */
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| 45 | export declare function pairwise<T>(): OperatorFunction<T, [T, T]>;
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