partitionMany

partitions.ts

import {marbles} from "rxjs-marbles";


export function partitions<T>(
  source: ObservableInput<T>,
  p1: ((value: T, index: number) => boolean),
): [Observable<T>, Observable<T>] ;
export function partitions<T>(
  source: ObservableInput<T>,
  p1: ((value: T, index: number) => boolean),
  p2: ((value: T, index: number) => boolean),
): [Observable<T>, Observable<T>, Observable<T>] ;
export function partitions<T>(
  source: ObservableInput<T>,
  p1: ((value: T, index: number) => boolean),
  p2: ((value: T, index: number) => boolean),
  p3: ((value: T, index: number) => boolean),
): [Observable<T>, Observable<T>, Observable<T>, Observable<T>] ;
export function partitions<T>(
  source: ObservableInput<T>,
  p1: ((value: T, index: number) => boolean),
  p2: ((value: T, index: number) => boolean),
  p3: ((value: T, index: number) => boolean),
  p4: ((value: T, index: number) => boolean),
): [Observable<T>, Observable<T>, Observable<T>, Observable<T>, Observable<T>] ;
export function partitions<T>(
  source: ObservableInput<T>,
  ...predicates: ((value: T, index: number) => boolean)[]
): Observable<T>[] {
  if(predicates.length===0)
    throw new Error('No predicates provided');
  return predicates.reduce((result, p) => {
    const last = result[result.length - 1];
    const partitioned = partition(last, p);
    result.splice(result.length - 1, 1, ...partitioned);
    return result;
  }, [source] as Observable<T>[]);
}

describe('partitions', () => {
  it('works just like partition for single predicate', marbles(m => {

    const source = m.hot("^-1-2-3-4-5|");

    const [even, odd] = partitions(source, v => v % 2 == 0);

    m.expect(odd).toBeObservable('^-1---3---5|');
    m.expect(even).toBeObservable('^---2---4--|');
  }));

  it('multiple predicates create sequences by recursively partitioning the stream', marbles(m => {

    const source = m.hot("^-1-2-3-4-5-6-7|");

    const [even__, divBy3, odd___] = partitions(
      source,
      v => v % 2 == 0, // split source into [even, odd]
      v => v % 3 == 0  // split odd into [divisible by 3, rest of the odd numbers]
    );

    m.expect(even__).toBeObservable('^---2---4---6--|');
    m.expect(divBy3).toBeObservable('^-----3--------|');
    m.expect(odd___).toBeObservable('^-1-------5---7|');
  }))
})