groupBy (Functional Programming)

Creates a function that groups values by a key. Use it with pipe.

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

::: info

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

:::

Usage

groupBy calls getKey for each value in the piped array and returns an object whose keys are the returned keys and whose values are arrays of matching items.

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

pipe(
  ['one', 'two', 'three'],
  groupBy(word => word.length)
); // => { 3: ['one', 'two'], 5: ['three'] }

Parameters

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

Returns

((array: readonly T[]) => Record<K, T[]>): A function that maps a readonly T[] to grouped arrays by key.