groupBy
function stable operator
groupBy<T, K, R>(keySelector: (value: T) => K, elementOrOptions?: void | ((value: any) => any) | BasicGroupByOptions<K, T> | GroupByOptionsWithElement<K, R, T>, duration?: (grouped: GroupedObservable<any, any>) => ObservableInput<any>, connector?: () => SubjectLike<any>): OperatorFunction<T, GroupedObservable<K, R>>
Parameters
keySelector |
(value: T) => K |
|
elementOrOptions |
void | ((value: any) => any) | BasicGroupByOptions<K, T> | GroupByOptionsWithElement<K, R, T> |
Optional. Default is |
duration |
(grouped: GroupedObservable<any, any>) => ObservableInput<any> |
Optional. Default is |
connector |
() => SubjectLike<any> |
Optional. Default is |
Returns
OperatorFunction<T, GroupedObservable<K, R>>
Overloads
groupBy(key: (value: T) => K, options: BasicGroupByOptions<K, T>): OperatorFunction<T, GroupedObservable<K, T>>
Parameters
key |
(value: T) => K |
|
options |
BasicGroupByOptions<K, T> |
Returns
OperatorFunction<T, GroupedObservable<K, T>>
groupBy(key: (value: T) => K, options: GroupByOptionsWithElement<K, E, T>): OperatorFunction<T, GroupedObservable<K, E>>
Parameters
key |
(value: T) => K |
|
options |
GroupByOptionsWithElement<K, E, T> |
Returns
OperatorFunction<T, GroupedObservable<K, E>>
groupBy(key: (value: T) => value is K): OperatorFunction<T, GroupedObservable<true, K> | GroupedObservable<false, Exclude<T, K>>>
Parameters
key |
(value: T) => value is K |
Returns
OperatorFunction<T, GroupedObservable<true, K> | GroupedObservable<false, Exclude<T, K>>>
groupBy(key: (value: T) => K): OperatorFunction<T, GroupedObservable<K, T>>
Parameters
key |
(value: T) => K |
Returns
OperatorFunction<T, GroupedObservable<K, T>>
groupBy(key: (value: T) => K, element: void, duration: (grouped: GroupedObservable<K, T>) => Observable<any>): OperatorFunction<T, GroupedObservable<K, T>>
Parameters
key |
(value: T) => K |
|
element |
void |
|
duration |
(grouped: GroupedObservable<K, T>) => Observable<any> |
Returns
OperatorFunction<T, GroupedObservable<K, T>>
groupBy(key: (value: T) => K, element?: (value: T) => R, duration?: (grouped: GroupedObservable<K, R>) => Observable<any>): OperatorFunction<T, GroupedObservable<K, R>>
Parameters
key |
(value: T) => K |
|
element |
(value: T) => R |
Optional. Default is |
duration |
(grouped: GroupedObservable<K, R>) => Observable<any> |
Optional. Default is |
Returns
OperatorFunction<T, GroupedObservable<K, R>>
groupBy(key: (value: T) => K, element?: (value: T) => R, duration?: (grouped: GroupedObservable<K, R>) => Observable<any>, connector?: () => Subject<R>): OperatorFunction<T, GroupedObservable<K, R>>
Groups the items emitted by an Observable according to a specified criterion, and emits these grouped items as GroupedObservables, one GroupedObservable per group.
Parameters
key |
(value: T) => K |
A function that extracts the key for each item. |
element |
(value: T) => R |
Optional. Default is A function that extracts the return element for each item. |
duration |
(grouped: GroupedObservable<K, R>) => Observable<any> |
Optional. Default is A function that returns an Observable to determine how long each group should exist. |
connector |
() => Subject<R> |
Optional. Default is Factory function to create an intermediate Subject through which grouped elements are emitted. |
Returns
OperatorFunction<T, GroupedObservable<K, R>>: A function that returns an Observable that emits GroupedObservables, each of which corresponds to a unique key value and each of which emits those items from the source Observable that share that key value.
When the Observable emits an item, a key is computed for this item with the key function.
If a GroupedObservable for this key exists, this GroupedObservable emits. Otherwise, a new GroupedObservable for this key is created and emits.
A GroupedObservable represents values belonging to the same group represented by a common key. The common key is available as the key field of a GroupedObservable instance.
The elements emitted by GroupedObservables are by default the items emitted by the Observable, or elements returned by the element function.
Examples
Group objects by id and return as array
import { of, groupBy, mergeMap, reduce } from 'rxjs';
of(
{ id: 1, name: 'JavaScript' },
{ id: 2, name: 'Parcel' },
{ id: 2, name: 'webpack' },
{ id: 1, name: 'TypeScript' },
{ id: 3, name: 'TSLint' }
).pipe(
groupBy(p => p.id),
mergeMap(group$ => group$.pipe(reduce((acc, cur) => [...acc, cur], [])))
)
.subscribe(p => console.log(p));
// displays:
// [{ id: 1, name: 'JavaScript' }, { id: 1, name: 'TypeScript'}]
// [{ id: 2, name: 'Parcel' }, { id: 2, name: 'webpack'}]
// [{ id: 3, name: 'TSLint' }]
Pivot data on the id field
import { of, groupBy, mergeMap, reduce, map } from 'rxjs';
of(
{ id: 1, name: 'JavaScript' },
{ id: 2, name: 'Parcel' },
{ id: 2, name: 'webpack' },
{ id: 1, name: 'TypeScript' },
{ id: 3, name: 'TSLint' }
).pipe(
groupBy(p => p.id, { element: p => p.name }),
mergeMap(group$ => group$.pipe(reduce((acc, cur) => [...acc, cur], [`${ group$.key }`]))),
map(arr => ({ id: parseInt(arr[0], 10), values: arr.slice(1) }))
)
.subscribe(p => console.log(p));
// displays:
// { id: 1, values: [ 'JavaScript', 'TypeScript' ] }
// { id: 2, values: [ 'Parcel', 'webpack' ] }
// { id: 3, values: [ 'TSLint' ] }
© 2015–2022 Google, Inc., Netflix, Inc., Microsoft Corp. and contributors.
Code licensed under an Apache-2.0 License. Documentation licensed under CC BY 4.0.
https://rxjs.dev/api/index/function/groupBy
