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.