import { identity } from "../../function/identity.mjs";
import { iteratee } from "../util/iteratee.mjs";
import { sumBy } from "./sumBy.mjs";
//#region src/compat/math/meanBy.ts
/**
* Calculates the average of an array of numbers when applying
* the `iteratee` function to each element.
*
* If the array is empty, this function returns `NaN`.
*
* If the key is missing or the value is `undefined`, it is treated as `0`.
* However, if every value is `undefined`, the result is `NaN`.
*
* @template T - The type of elements in the array.
* @param items An array to calculate the average.
* @param iteratee
* The criteria used to determine the maximum value.
*  - If a **function** is provided, it extracts a numeric value from each element.
*  - If a **string** is provided, it is treated as a key to extract values from the objects.
*  - If a **[key, value]** pair is provided, it matches elements with the specified key-value pair.
*  - If an **object** is provided, it matches elements that contain the specified properties.
* @returns The average of all the numbers as determined by the `iteratee` function.
*
* @example
* meanBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: 2
* meanBy([], x => x.a); // Returns: NaN
* meanBy([[2], [3], [1]], 0); // Returns: 2
* meanBy([{ a: 2 }, { a: 3 }, { a: 1 }], 'a'); // Returns: 2
* meanBy([{ a: 1 }, {}], 'a'); // Returns: 0.5
*/
function meanBy(items, iteratee$1) {
	const length = items == null ? 0 : items.length;
	if (!length) return NaN;
	return sumBy(items, iteratee(iteratee$1 ?? identity)) / length;
}
//#endregion
export { meanBy };
