# Sort an array randomly in JavaScript

Let's assume that you have the following array:

```javascript```let array = [1, 2, 3, 4];
``````

You can sort it randomly by:

```javascript```let shuffle = array.map((e, i, a) => {

// Getting a random value between [i, a.length]
// Math.floor can be translated as ~~
let j = Math.floor(Math.random() * (a.length - i) + i);

// Switching the elements of positions i & j
[a[i], a[j]] = [a[j], a[i]];

// Returning current value
return a[i];

});

console.log(shuffle);
// [4, 2, 3, 1]
``````

In one line of code:

```javascript```let shuffle = array.map((e, i, a, j = ~~(Math.random() * (a.length - i) + i)) => ([a[i], a[j]] = [a[j], a[i]], a[i]));
``````

## Testing the function

Now you need to check if the distribution is uniform. Create a test of the function and generate the random array a several number of times:

```javascript```let test = {};

for(let i = 0; i < 10000; i ++){

let array   = [1, 2, 3, 4];
let shuffle = array.map((e, i, a, j = ~~(Math.random() * (a.length - i) + i)) => ([a[i], a[j]] = [a[j], a[i]], a[i]));

let string  = shuffle.join('');

if(test[string] >= 0) test[string] ++;
else                  test[string] = 0;

}
``````

Here you have the total times an array has been created.

For example, the array `[1, 2, 4, 3]` has been created 396 times.

``````console.log(test);
/*
1234: 418
1243: 396
1324: 425
1342: 364
1423: 420
1432: 396
2134: 434
2143: 413
2314: 399
2341: 429
2413: 423
2431: 395
3124: 351
3142: 434
3214: 409
3241: 448
3412: 421
3421: 451
4123: 397
4132: 429
4213: 437
4231: 428
4312: 429
4321: 430
*/
``````

It looks like a uniform distribution, because all the possible results have been created with equal probabilty. Hi, I'm Erik, an engineer from Barcelona. If you like the post or have any comments, say hi.