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feat(groupBy): add seed option to eagerly create groups #6425

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54 changes: 50 additions & 4 deletions spec/operators/groupBy-spec.ts
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Original file line number Diff line number Diff line change
@@ -1,9 +1,10 @@
import { expect } from 'chai';
import { groupBy, delay, tap, map, take, mergeMap, materialize, skip, ignoreElements } from 'rxjs/operators';
import { TestScheduler } from 'rxjs/testing';
import { ReplaySubject, of, Observable, Operator, Observer, interval, Subject } from 'rxjs';
import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
import { Observable, Observer, of, Operator, ReplaySubject, Subject } from 'rxjs';
import { createNotification } from 'rxjs/internal/NotificationFactories';
import { delay, groupBy, ignoreElements, map, materialize, mergeMap, skip, take, tap } from 'rxjs/operators';
import { TestScheduler } from 'rxjs/testing';
import { cold, expectObservable, expectSubscriptions, hot } from '../helpers/marble-testing';
import { observableMatcher } from '../helpers/observableMatcher';

declare const rxTestScheduler: TestScheduler;

Expand Down Expand Up @@ -1456,6 +1457,51 @@ describe('groupBy operator', () => {

expect(sideEffects).to.deep.equal([0, 1, 2]);
});

describe('seed', () => {
let rxTest: TestScheduler;

beforeEach(() => {
rxTest = new TestScheduler(observableMatcher);
});

it('should open groups when seed emits', () => {
rxTest.run(({ cold, expectObservable, expectSubscriptions }) => {
const source = cold('(--)---a---| ');
const sourceSubs = ' (^-)-------! ';
const seed = cold(' (ab)----------|');
const seedSubs = ' (^-)-------! ';
const expected = ' (ab)-------| ';
const a = cold(' (--)---a---| ');
const b = cold(' (--)-------| ');
const expectedValues = { a, b };

const grouped = source.pipe(groupBy((letter) => letter, { seed: () => seed }));

expectObservable(grouped).toBe(expected, expectedValues);
expectSubscriptions(source.subscriptions).toBe(sourceSubs);
expectSubscriptions(seed.subscriptions).toBe(seedSubs);
});
});

it('should emit complete when the seed completes', () => {
rxTest.run(({ cold, expectObservable, expectSubscriptions }) => {
const source = cold('(--)---a---|');
const sourceSubs = ' (^-)-------!';
const seed = cold(' (a|) ');
const seedSubs = ' (^!) ';
const expected = ' (a|) ';
const a = cold(' (--)---a---|');
const expectedValues = { a };

const grouped = source.pipe(groupBy((letter) => letter, { seed: () => seed }));

expectObservable(grouped).toBe(expected, expectedValues);
expectSubscriptions(source.subscriptions).toBe(sourceSubs);
expectSubscriptions(seed.subscriptions).toBe(seedSubs);
});
});
})
});

/**
Expand Down
96 changes: 56 additions & 40 deletions src/internal/operators/groupBy.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9,12 +9,14 @@ interface BasicGroupByOptions<K, T> {
element?: undefined;
duration?: (grouped: GroupedObservable<K, T>) => ObservableInput<any>;
connector?: () => SubjectLike<T>;
seed?: () => ObservableInput<K>;
}

interface GroupByOptionsWithElement<K, E, T> {
element: (value: T) => E;
duration?: (grouped: GroupedObservable<K, E>) => ObservableInput<any>;
connector?: () => SubjectLike<E>;
seed?: () => ObservableInput<K>;
}

export function groupBy<T, K>(key: (value: T) => K, options: BasicGroupByOptions<K, T>): OperatorFunction<T, GroupedObservable<K, T>>;
Expand Down Expand Up @@ -155,10 +157,11 @@ export function groupBy<T, K, R>(
): OperatorFunction<T, GroupedObservable<K, R>> {
return operate((source, subscriber) => {
let element: ((value: any) => any) | void;
let seed: (() => ObservableInput<K>) | undefined;
if (!elementOrOptions || typeof elementOrOptions === 'function') {
element = elementOrOptions;
} else {
({ duration, element, connector } = elementOrOptions);
({ duration, element, connector, seed } = elementOrOptions);
}

// A lookup for the groups that we have so far.
Expand Down Expand Up @@ -189,45 +192,7 @@ export function groupBy<T, K, R>(
// OperatorSubscriber will only send the error to the main subscriber.
try {
const key = keySelector(value);

let group = groups.get(key);
if (!group) {
// Create our group subject
groups.set(key, (group = connector ? connector() : new Subject<any>()));

// Emit the grouped observable. Note that we can't do a simple `asObservable()` here,
// because the grouped observable has special semantics around reference counting
// to ensure we don't sever our connection to the source prematurely.
const grouped = createGroupedObservable(key, group);
subscriber.next(grouped);

if (duration) {
const durationSubscriber = new OperatorSubscriber(
// Providing the group here ensures that it is disposed of -- via `unsubscribe` --
// wnen the duration subscription is torn down. That is important, because then
// if someone holds a handle to the grouped observable and tries to subscribe to it
// after the connection to the source has been severed, they will get an
// `ObjectUnsubscribedError` and know they can't possibly get any notifications.
group as any,
() => {
// Our duration notified! We can complete the group.
// The group will be removed from the map in the teardown phase.
group!.complete();
durationSubscriber?.unsubscribe();
},
// Completions are also sent to the group, but just the group.
undefined,
// Errors on the duration subscriber are sent to the group
// but only the group. They are not sent to the main subscription.
undefined,
// Teardown: Remove this group from our map.
() => groups.delete(key)
);

// Start our duration notifier.
groupBySourceSubscriber.add(innerFrom(duration(grouped)).subscribe(durationSubscriber));
}
}
const group = groups.get(key) ?? createGroup(key);

// Send the value to our group.
group.next(element ? element(value) : value);
Expand All @@ -246,9 +211,60 @@ export function groupBy<T, K, R>(
() => groups.clear()
);

if (seed !== undefined) {
groupBySourceSubscriber.add(
innerFrom(seed()).subscribe({
next: (value) => void (groups.has(value) || createGroup(value)),
complete: () => subscriber.complete(),
error: handleError,
})
);
}

// Subscribe to the source
source.subscribe(groupBySourceSubscriber);

function createGroup(key: K): SubjectLike<T> {
// Create our group subject
const group = connector ? connector() : new Subject<any>();
groups.set(key, group);

// Emit the grouped observable. Note that we can't do a simple `asObservable()` here,
// because the grouped observable has special semantics around reference counting
// to ensure we don't sever our connection to the source prematurely.
const grouped = createGroupedObservable(key, group);
subscriber.next(grouped);

if (duration) {
const durationSubscriber = new OperatorSubscriber(
// Providing the group here ensures that it is disposed of -- via `unsubscribe` --
// when the duration subscription is torn down. That is important, because then
// if someone holds a handle to the grouped observable and tries to subscribe to it
// after the connection to the source has been severed, they will get an
// `ObjectUnsubscribedError` and know they can't possibly get any notifications.
group as any,
() => {
// Our duration notified! We can complete the group.
// The group will be removed from the map in the teardown phase.
group.complete();
durationSubscriber.unsubscribe();
},
// Completions are also sent to the group, but just the group.
undefined,
// Errors on the duration subscriber are sent to the group
// but only the group. They are not sent to the main subscription.
undefined,
// Teardown: Remove this group from our map.
() => groups.delete(key)
);

// Start our duration notifier.
groupBySourceSubscriber.add(innerFrom(duration(grouped)).subscribe(durationSubscriber));
}

return group;
}

/**
* Creates the actual grouped observable returned.
* @param key The key of the group
Expand Down