Selecting a random amount of elements from array in javascript

Question

I have 2 arrays with 4 x-coordinates in each. In total I want to select 3 random values from both arrays. So array1+array2 =3 elements. In the end i just done it a bad way to make it do what i wanted. Just wondering if anyone can see a more efficient way to produce nicer code. This is how i ended up getting it to work. I cant show what i have tried as it has been so modified i ended up just deleting it and doing this.

enemyCars = [100, 200, 300, 400];    //not actual values

newCarArray = [];    //global
newWallArray = [];    //global

function randomNumber(a, b){
    return Math.round(random(a,b));
}

function chooseCars(){
    let carAmount = randomNumber(0,3);
    let wallAmount = 3 - carAmount;
    print('carAmount ' + carAmount);

    if(carAmount == 0){
        newCarArray = [];
    }
    if(carAmount == 1){
        let a = randomNumber(0,3);
        newCarArray.push(enemyCars[a]);
    }
    if(carAmount == 2){
        let a = randomNumber(0,3);
        newCarArray.push(enemyCars[a]);
        let b = randomNumber(0,3);
        newCarArray.push(enemyCars[b]);
    }
    if(carAmount == 3){
        let a = randomNumber(0,3);
        newCarArray.push(enemyCars[a]);
        let b = randomNumber(0,3);
        newCarArray.push(enemyCars[b]);
        let c = randomNumber(0,3);
        newCarArray.push(enemyCars[c]);
    }

    if(wallAmount == 0){
        newWallArray = [];
    }
    if(wallAmount == 1){
        let a = randomNumber(0,3);
        newWallArray.push(enemyWalls[a]);
    }
    if(wallAmount == 2){
        let a = randomNumber(0,3);
        newWallArray.push(enemyWalls[a]);
        let b = randomNumber(0,3);
        newWallArray.push(enemyWalls[b]);
    }
    if(wallAmount == 3){
        let a = randomNumber(0,3);
        newWallArray.push(enemyWalls[a]);
        let b = randomNumber(0,3);
        newWallArray.push(enemyWalls[b]);
        let c = randomNumber(0,3);
        newWallArray.push(enemyWalls[c]);
    }
}

thanks for the help

Does this answer your question? [Getting a random value from a JavaScript array](https://stackoverflow.com/questions/4550505/getting-a-random-value-from-a-javascript-array) — Liam, Dec 17 '19 at 09:03
I think this would be better here https://codereview.stackexchange.com/. Since you already have a working solution. — Cosmin_Victor, Dec 17 '19 at 09:03
Where is the second array in your code? I only see one: `enemyCars ` — Brett Gregson, Dec 17 '19 at 09:09
these are both the arrays i want to fill. enemyCars is the source for both. `newCarArray = []; //global newWallArray = []; //global` — Matthew Reid, Dec 17 '19 at 09:21

score 1 · Answer 1 · answered Dec 17 '19 at 09:41

Thanks for the help I was finally able to create some nicer code. always seem to overcomplicate things and can't see the simple solution. Thanks @JonasWilms

function abc(){
    let carAmount = randomNumber(0,3);
    let wallAmount = 3 - carAmount;
    print('carAmount ' + carAmount);
    print('wallAmount ' + wallAmount);
    let enemyCoord = [...enemyCars];
    //print(enemyCoord);
    newCarArray = [];
    newWallArray = [];

    for(let i = 0; i < carAmount; i++) {
        let a = randomNumber(0,enemyCoord.length-1)
        newCarArray.push(enemyCars[a]);
        delete enemyCoord[a];
        filterArray(enemyCoord);
    }
    for(let i = 0; i <wallAmount; i++){
        let a = randomNumber(0,enemyCoord.length-1)
        newWallArray.push(enemyWalls[a]);
        delete enemyCoord[a];
        filterArray(enemyCoord);
    }
    print(newCarArray);
    print(newWallArray);
}

You can go one step further and refactor the loops into a function, send the number of loops as parameters (carAmount, WallAmount) and then return the new Array. `let newCarArray = randomizeFromEnemyCoord(carAmount)` — Rickard Elimää, Dec 17 '19 at 10:03

score 1 · Answer 2 · answered Dec 17 '19 at 11:54

1

Here's a short code that merges two arrays into a single array, shuffles it randomly, and then give you the first three values from the array:

var randoms = randoSequence([1, 2, 3, 4].concat([5, 6, 7, 8])).splice(0, 3)
randoms.forEach(function(p, i, a){a[i]=a[i]["value"]});

console.log(randoms);

<script src="https://randojs.com/1.0.0.js"></script>

Notice the second line. https://randojs.com gives you an array of objects with BOTH indices and values, but we're only interested in the values.

answered Dec 17 '19 at 11:54

Aaron Plocharczyk

2,776
2
7
15

Am I correct to assume I can replace the [1,2,3,4] & [5,6,7,8] with the array variable name of each array and then the splice starts at index 0 and removes the first 3 from the array and stores them in randoms variable? – Matthew Reid Dec 17 '19 at 13:59

score 0 · Accepted Answer · answered Dec 17 '19 at 09:22

0

All you need is a loop:

 for(let count = 0; count < carAmount; count++) {
    newCarArray.push(enemyCars[ randomNumber(0, 3) ]);
 }

answered Dec 17 '19 at 09:22

Jonas Wilms

132,000
20
149
151

Selecting a random amount of elements from array in javascript

3 Answers3