@rx-angular/state/selections

A set of RxJS operators for selecting state in an efficient, distinct way. They are the building blocks RxState uses internally for its select surface, and they are exported so you can use them directly inside your own RxJS pipelines.

Motivation

For reading state inside a component, prefer native signals (state.signal('key') and computed()) over these operators. A computed() is glitch-free and distinct-by-value with no operator plumbing, and it does not require an | async subscription.

These operators are for RxJS pipelines: composing multiple Observable sources, gating a stream on a subset of keys before it reaches state, or feeding a connect. That is the residual niche where distinct-checked, replayed selection still earns its place. See Reactive state: global vs local, RxState + signals for when in-component derivation belongs in a signal versus a pipeline.

Operators

Operator	Purpose
select	Read a slice of state as a shared, replayed, distinct Observable. Overloads for whole-state, operator composition, deep-key access, and key/slice projection.
selectSlice	Emit only the provided keys, filtered to defined values and checked distinct, always a complete slice.
distinctUntilSomeChanged	Emit items that are distinct by comparison across the given keys (via Array.prototype.some), with an optional per-key compare map.
stateful	Turn a plain Observable into a stateful one: filtered to defined values, distinct, and shared/replayed.

Interfaces

Interface	Purpose
CompareFn	Signature of a custom equality comparator.
KeyCompareMap	Map of per-key CompareFns used by the distinct operators.

Import

import { select, selectSlice, distinctUntilSomeChanged, stateful } from '@rx-angular/state/selections';

See also

• Concept: Reactive state: global vs local, RxState + signals
• Reference: RxState (functional)