meanBy

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

const average = meanBy(items, getValue);

Reference

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

• items (readonly T[]): An array to calculate the average.
• getValue ((element: T) => number): A function that selects a numeric value from each element.

Returns

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