How to generate a random weighted distribution of elements

Question

I would like to return an array which has a set of unique elements randomly distributed according to custom frequency. My real world use-case is the repetition of carousel i

Answer 1

Let's say you take your distribution numbers as an array of objects, like this:

var items = [
    {item: "A", weight: 20}, 
    {item: "B", weight: 50}, 
    {item: "C", weight: 80},
    {item: "D", weight: 10}
];

This removes any assumption that your weights add up to 100% - they might be click-counts, or votes, or any other value you like. Then you can do this:

function weightedSelect(items) {
    // Get the total, and make the weights cummulative
    var total = items.reduce(function(sum, item){
        item.weight = item.weight + sum;
        return item.weight;
    },0);

    var r = Math.random() * total;

    // Can't use .forEach() here because we want early termination
    for (var i = 0; i < items.length; i++) {
         if (r < items[i].weight)
             return items[i].item;
    }
}

I'm not sure how this compares to the other implementations for efficiency, but it's concise.