uniqBy (Functional Programming)

Creates a function that removes duplicates by a mapped key. Use it with pipe.

typescript

const result = pipe(array, uniqBy(mapper));

::: info

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

:::

Usage

uniqBy keeps the first value for each key returned by mapper. It preserves the order of first occurrence and is lazy-capable inside pipe.

typescript

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

pipe(
  [{ id: 1 }, { id: 1 }, { id: 2 }],
  uniqBy(item => item.id)
); // => [{ id: 1 }, { id: 2 }]

mapper ((item: T, index: number) => U): The function that returns the key used for uniqueness.

((array: readonly T[]) => T[]): A function that maps a readonly T[] to a duplicate-free array by key.