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/math/meanBy.md.
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    meanBy es-toolkit

    Calculates the average of an array by applying the getValue function to each element.

    const average = meanBy(items, getValue);

    Usage

    meanBy(items, getValue)

    Use meanBy when you want to find the average of the results of applying a function to each element of an array. It's useful for calculating the average of a specific property from an array of objects or for finding the average after transforming each element. If given an empty array, it returns NaN.

    import { meanBy } from 'es-toolkit/math';

// Calculate the average of a specific property from an array of objects
const people = [{ age: 23 }, { age: 25 }, { age: 27 }];
const averageAge = meanBy(people, person => person.age);
// averageAge is 25 ((23 + 25 + 27) / 3 = 75 / 3 = 25)

// Calculate the average of string lengths
const words = ['apple', 'banana', 'cherry'];
const averageLength = meanBy(words, word => word.length);
// averageLength is approximately 5.67 ((5 + 6 + 6) / 3 ≈ 5.67)

// Returns NaN for an empty array
const emptyResult = meanBy([], x => x);
// emptyResult is NaN

    Parameters

    itemsreadonly T[]required

    An array to calculate the average.

    getValue(element: T) => numberrequired

    A function that selects a numeric value from each element.

    Returns

    Returns the average of all values as determined by the getValue function. Returns NaN if the array is empty.

    number
    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.