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/array/unzipWith.md.
Install massaman

    unzipWith es-toolkit

    Unpacks grouped arrays and applies a transformation function to return a new array.

    const transformedArray = unzipWith(target, iteratee);

    Usage

    unzipWith(target, iteratee)

    Use unzipWith when you want to collect elements at the same position from a 2D array where multiple arrays are grouped together and apply a transformation function to get the result. It's similar to unzip but allows you to transform the elements in each group with a custom function.

    import { unzipWith } from 'es-toolkit/array';

// Add numbers at the same position.
const numbers = [
  [1, 2],
  [3, 4],
  [5, 6],
];
const sums = unzipWith(numbers, (a, b, c) => a + b + c);
console.log(sums); // [9, 12] (1+3+5=9, 2+4+6=12)

// Concatenate strings at the same position.
const words = [
  ['hello', 'world'],
  ['foo', 'bar'],
  ['es', 'toolkit'],
];
const combined = unzipWith(words, (a, b, c) => a + b + c);
console.log(combined); // ['hellofooes', 'worldbartoolkit']

// Calculate average of specific property from object array.
const scores = [
  [{ score: 80 }, { score: 90 }],
  [{ score: 85 }, { score: 95 }],
  [{ score: 75 }, { score: 88 }],
];
const averages = unzipWith(scores, (a, b, c) => (a.score + b.score + c.score) / 3);
console.log(averages); // [80, 91] (80+85+75)/3, (90+95+88)/3

    If arrays have different lengths, undefined is passed.

    import { unzipWith } from 'es-toolkit/array';

const mixed = [
  [1, 4],
  [2, 5],
  [3], // Different length
];
const result = unzipWith(mixed, (a, b, c) => {
  // c can be undefined
  return (a || 0) + (b || 0) + (c || 0);
});
console.log(result); // [6, 9] (1+2+3, 4+5+0)

    Passing an empty array will throw an error.

    import { unzipWith } from 'es-toolkit/array';

const empty = unzipWith([], (a, b) => a + b);
console.log(empty); // throws Error

    Parameters

    targetreadonly T[][]required

    A 2D array where multiple arrays are grouped together to be unpacked and transformed.

    iteratee(...args: T[]) => Rrequired

    A function that receives elements at the same position and transforms them into a new value.

    Returns

    A new array created by applying the transformation function to the results.

    R[]
    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.