keyBy (Functional Programming)

Creates a function that builds an object keyed by each value. Use it with pipe.

const result = pipe(array, keyBy(getKey));

::: info

Prefer the original es-toolkit keyBy in ordinary code. Use this fp variant when composing transformations with pipe.

:::

Usage

keyBy calls getKey for each value in the piped array and returns an object whose keys are the returned keys and whose values are the original items. Later values overwrite earlier values with the same key.

import { keyBy, pipe } from 'es-toolkit/fp';

pipe(
  [
    { id: 'a', value: 1 },
    { id: 'b', value: 2 },
  ],
  keyBy(item => item.id)
); // => { a: { id: 'a', value: 1 }, b: { id: 'b', value: 2 } }

Parameters

• getKey ((item: T) => K): The function that returns the key for each value.

Returns

((array: readonly T[]) => Record<K, T>): A function that maps a readonly T[] to an object keyed by getKey.