weightedRandom

weightedRandom.js

function weightedRandom(ar) {
	var ar = ar.sort(x => x.w);
	var sum = ar.reduce((p, c) => p + c.w, 0);
	// normalise
	var soFar = 0;
	ar.map(o => {
		o.w = o.w / sum;
		o.w += soFar;
		soFar += o.w;
	});
	var item, r = Math.random();
	while ((item = ar.shift()) && r > item.w);
	return item && item.w;
}