import { distinctUntilChanged } from './distinctUntilChanged';
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import { MonoTypeOperatorFunction } from '../types';
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/* tslint:disable:max-line-length */
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export function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>;
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export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T>;
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/* tslint:enable:max-line-length */
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/**
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* Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item,
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* using a property accessed by using the key provided to check if the two items are distinct.
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*
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* If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
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*
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* If a comparator function is not provided, an equality check is used by default.
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*
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* ## Examples
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*
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* An example comparing the name of persons
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*
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* ```ts
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* import { of, distinctUntilKeyChanged } from 'rxjs';
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*
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* of(
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* { age: 4, name: 'Foo' },
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* { age: 7, name: 'Bar' },
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* { age: 5, name: 'Foo' },
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* { age: 6, name: 'Foo' }
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* ).pipe(
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* distinctUntilKeyChanged('name')
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* )
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* .subscribe(x => console.log(x));
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*
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* // displays:
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* // { age: 4, name: 'Foo' }
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* // { age: 7, name: 'Bar' }
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* // { age: 5, name: 'Foo' }
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* ```
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*
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* An example comparing the first letters of the name
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*
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* ```ts
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* import { of, distinctUntilKeyChanged } from 'rxjs';
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*
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* of(
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* { age: 4, name: 'Foo1' },
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* { age: 7, name: 'Bar' },
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* { age: 5, name: 'Foo2' },
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* { age: 6, name: 'Foo3' }
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* ).pipe(
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* distinctUntilKeyChanged('name', (x, y) => x.substring(0, 3) === y.substring(0, 3))
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* )
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* .subscribe(x => console.log(x));
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*
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* // displays:
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* // { age: 4, name: 'Foo1' }
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* // { age: 7, name: 'Bar' }
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* // { age: 5, name: 'Foo2' }
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* ```
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*
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* @see {@link distinct}
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* @see {@link distinctUntilChanged}
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*
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* @param {string} key String key for object property lookup on each item.
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* @param {function} [compare] Optional comparison function called to test if an item is distinct from the previous item in the source.
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* @return A function that returns an Observable that emits items from the
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* source Observable with distinct values based on the key specified.
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*/
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export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare?: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T> {
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return distinctUntilChanged((x: T, y: T) => compare ? compare(x[key], y[key]) : x[key] === y[key]);
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}
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