// ==UserScript==
// @name         IMDb Standard Deviation
// @namespace    http://userscripts.org/users/7063
// @include      https://www.imdb.com/title/tt*/ratings
// @include      https://www.imdb.com/title/tt*/ratings-*
// @include      https://www.imdb.com/title/tt*/ratings?*
// @version      2018.12.8.11.39
// @grant        none
// @description  Adds standard deviation to IMDb ratings breakdown pages.
// @downloadURL none
// ==/UserScript==

/*eslint-env browser*/

"use strict";
(function () {
	const main = document.querySelector("#main");
	if (!main) {
		return;
	}
	const votes = [...main.querySelector("table").rows].map(
		k => k.cells[2].textContent.replace(/[\s,]+/g, ""));
	votes.shift();//
	let product = 0;
	let votecount = 0;
	votes.forEach((v, i) => {
		product += v * (10 - i);
		votecount += +v;
	});
	const sumOfSquares = votes.reduce((p, c, i) => p +
		Math.pow(10 - i - product / votecount, 2) * c, 0);
	main.querySelector(".title-ratings-sub-page .allText[align=\"center\"]").textContent +=
		`\xA0 Standard Deviation = ${Math.sqrt(sumOfSquares / (votecount - 1)).toFixed(2)}`;
}());