For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/fp/keyBy.md.
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    keyBy (Functional Programming) es-toolkit

    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) => Krequired

    The function that returns the key for each value.

    Returns

    A function that maps a readonly T[] to an object keyed by getKey.

    (array: readonly T[]) => Record<K, T>
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.