/* @flow */

import sum from "./sum";

/**
 * The mean, _also known as average_,
 * is the sum of all values over the number of values.
 * This is a [measure of central tendency](https://en.wikipedia.org/wiki/Central_tendency):
 * a method of finding a typical or central value of a set of numbers.
 *
 * This runs on `O(n)`, linear time in respect to the array
 *
 * @param {Array<number>} x sample of one or more data points
 * @throws {Error} if the the length of x is less than one
 * @returns {number} mean
 * @example
 * mean([0, 10]); // => 5
 */
function mean(x /*: Array<number> */) /*: number */ {
    // The mean of no numbers is null
    if (x.length === 0) {
        throw new Error("mean requires at least one data point");
    }

    return sum(x) / x.length;
}

export default mean;