Select random value from a randomly selected array

Question

I'm an absolute novice when it comes to Javascript and Jquery. I'm trying to develop a system that will select a set number from an array.

I've got 3 arrays and a system that will select one of the numbers from these arrays.

var selectedArray = ["sixMatched","fiveMatched","fourMatched","threeMatched"];

    var sixMatched = ["367687"];

    var fiveMatched = ["567687","337687","167687","367587","368687"];

    var fourMatched = ["387087","357187","365627","367620","369627","867987","367610","367604","394687","397681","367247","167683","767697","567617","367207"];

    var threeMatched = ["338680","965647","163637","333677","837637","267427","364288","357634","767817","361557","302682","667027","320637","547686","967088","382637","360167","327286","817187","707087","387481","357280","563287","367803","867646","277686","384697","364483","467827","332681"];

I'm using the math.random function to select a random array name via the selectedArray array.

I want to then use the name picked from selectedArray and use that to select a random value from either sixMatched, fiveMatched, etc.

    $('#play').click(function(){
        var winningArray = selectedArray[Math.floor(Math.random()*selectedArray.length)];
        var winningNumber = winningArray[Math.floor(Math.random()*winningArray.length)];
        
        $('#number').animateNumber({ number: (winningNumber)});
        console.log("Winning array is "+ winningArray +"");
        console.log("Winning number is "+ winningNumber +"");
        return false;   
    });

What my code is doing though is selecting a random letter from winningArray rather than treating the value of the variable as a variable selector to then.

I was hoping that since winningArray would be set to for example "sixMatched" the code would select the sixMatched array and select a random value from it, but instead it's selecting a random letter from the value of winningArray instead.

Does anyone know how I can fix this?

Note that the chances of picking `367687` from `sixMatched` are substantially higher than `338680` from `threeMatched`. This is probably by design, but just wanted to point it out in case you aren't aware. For example consider array A `[1]` and B `[2,3]`. If I first pick a random array each array has a 50% chance. If I then pick a random number from the array you combine the chances. Meaning that I have a 50% chance to pick `1` (0.5 * 1), but `2` and `3` both have 25% chance of being picked (0.5 * 0.5). — 3limin4t0r, Jun 16 '23 at 15:18

score 0 · Accepted Answer · answered Jun 16 '23 at 14:58

Instead of separate top-level variables, make the arrays properties on an object:

var matchedArrays = {
  sixMatched: ["367687"],
  fiveMatched: ["567687","337687","167687","367587","368687"],
  fourMatched: ["387087","357187","365627","367620","369627","867987","367610","367604","394687","397681","367247","167683","767697","567617","367207"],
  threeMatched: ["338680","965647","163637","333677","837637","267427","364288","357634","767817","361557","302682","667027","320637","547686","967088","382637","360167","327286","817187","707087","387481","357280","563287","367803","867646","277686","384697","364483","467827","332681"]
};

Then you can use your randomly selected string value to reference the property on that object:

var winningNumber = matchedArrays[winningArray][Math.floor(Math.random()*matchedArrays[winningArray].length)];

Notice that the reference to winningArray was replaced with matchedArrays[winningArray], since winningArray itself is a string value and you can use strings to index object properties in JavaScript.

As an academic exercise at this point, you can get rid of the explicit selectedArray entirely and dynamically use the list of properties on the matchedArrays object, so you don't need to manually keep the two synchronized if they ever change.

score 0 · Answer 2 · answered Jun 16 '23 at 15:01

You are getting a random index of the string from selectedArray, not what you're looking for.

Consider using an Object with keys and values, then you just need to pick a random key for the 'array name'.

Since it's an object, you can easily target it's key's value to get the array, then get a random item from that array:

const allArrays = {
    sixMatched:  ["367687"],
    fiveMatched: ["567687","337687","167687","367587","368687"],
    fourMatched: ["387087","357187","365627","367620","369627","867987","367610","367604","394687","397681","367247","167683","767697","567617","367207"],
    threeMatched:["338680","965647","163637","333677","837637","267427","364288","357634","767817","361557","302682","667027","320637","547686","967088","382637","360167","327286","817187","707087","387481","357280","563287","367803","867646","277686","384697","364483","467827","332681"]
}

const allArrayKeys = Object.keys(allArrays);

var randomArrayKey = allArrayKeys[Math.floor(Math.random()*allArrayKeys.length)];
var randomArray    = allArrays[randomArrayKey]
var winningNumber = randomArray[Math.floor(Math.random()*randomArray.length)];

console.log("Winning array is "+ randomArrayKey +"");
console.log("Winning number is "+ winningNumber +"");

Select random value from a randomly selected array

2 Answers2