effect-io-ai

Package: effect
Module: Stream

Stream.partitionEither

Splits a stream into two substreams based on an effectful condition.

Details

The Stream.partitionEither function is used to divide a stream into two parts: one for elements that satisfy a condition producing Either.left values, and another for those that produce Either.right values. This function applies an effectful predicate to each element in the stream to determine which substream it belongs to.

The faster stream may advance up to bufferSize elements ahead of the slower one.

Example (Partitioning a Stream with an Effectful Predicate)

import { Effect, Either, Stream } from "effect"

const partition = Stream.range(1, 9).pipe(
  Stream.partitionEither(
    (n) => Effect.succeed(n % 2 === 0 ? Either.right(n) : Either.left(n)),
    { bufferSize: 5 }
  )
)

const program = Effect.scoped(
  Effect.gen(function*() {
    const [evens, odds] = yield* partition
    console.log(yield* Stream.runCollect(evens))
    console.log(yield* Stream.runCollect(odds))
  })
)

Effect.runPromise(program)
// { _id: 'Chunk', values: [ 1, 3, 5, 7, 9 ] }
// { _id: 'Chunk', values: [ 2, 4, 6, 8 ] }

See

• partition for partitioning a stream based on simple conditions.

Signature

declare const partitionEither: { <A, A3, A2, E2, R2>(predicate: (a: NoInfer<A>) => Effect.Effect<Either.Either<A3, A2>, E2, R2>, options?: { readonly bufferSize?: number | undefined; } | undefined): <E, R>(self: Stream<A, E, R>) => Effect.Effect<[left: Stream<A2, E2 | E, never>, right: Stream<A3, E2 | E, never>], E2 | E, Scope.Scope | R2 | R>; <A, E, R, A3, A2, E2, R2>(self: Stream<A, E, R>, predicate: (a: A) => Effect.Effect<Either.Either<A3, A2>, E2, R2>, options?: { readonly bufferSize?: number | undefined; } | undefined): Effect.Effect<[left: Stream<A2, E | E2, never>, right: Stream<A3, E | E2, never>], E | E2, Scope.Scope | R | R2>; }

Source

Since v2.0.0