Javascript get random variables from array but each just once

Question

I´d like to get random variables from a javascript and prepend it to a div container like that:

// my Array
var thumbnailArray = new Array();
thumbnailArray[0] = 'contentarray1';
thumbnailArray[1] = 'contentarray2';
thumbnailArray[2] = 'contentarray3';


function thumbnailquery () {
for (var i = 0; i <= 3; i++) {
$('#myDiv').prepend(thumbnailArray[Math.floor(Math.random() * thumbnailArray.length)])
}
}

Now how can i ensure that each variable is only taken once but still randomly?

Thank You

Do you have to leave the element in the array? If not, you could remove it from the array after it's been selected. — Corey Ogburn, Dec 10 '13 at 19:58

score 3 · Accepted Answer · answered Dec 10 '13 at 20:02

Shuffle the array and pop of values instead

function shuffle(a) {
  var c=a.length,t,r;
  while (0 !== c) {
    r = Math.floor(Math.random() * c);
    c -= 1;t = a[c];a[c] = a[r];a[r] = t;
  }
  return a;
}

var thumbnailArray = [
    'contentarray1',
    'contentarray2',
    'contentarray3'
];

shuffle( thumbnailArray );
thumbnailquery();

function thumbnailquery () {
    for (var i = 0; i <= 3; i++) {
       $('#myDiv').prepend( thumbnailArray.pop() );
    }
}

FIDDLE

score 1 · Answer 2 · answered Dec 10 '13 at 19:58

1

Copy the array. Then delete objects that you took from the copied array.

answered Dec 10 '13 at 19:58

Ramzi Khahil

4,932
4
35
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[`Array.prototype.splice()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice) for reference – jwueller Dec 10 '13 at 20:01

score 1 · Answer 3 · edited May 23 '17 at 12:23

There's no elegant way to do it the way you describe. You could construct an array of "selected indices" and ensure that each random number didn't already exist in that array, but that has a worst case operating time of infinity so highly not recommended.

Your best bet would be to shuffle the array and then iterate over, selecting the elements in order (shuffled order).

See this Stack Overflow for a good way to shuffle an array in JavaScript How can i shuffle an array in JavaScript?

score 1 · Answer 4 · answered Dec 10 '13 at 20:04

1

Use splice() http://www.w3schools.com/jsref/jsref_splice.asp

randNum = thumbnailArray[Math.floor(Math.random() * thumbnailArray.length)]
$('#myDiv').prepend(splice(randNum,1))

answered Dec 10 '13 at 20:04

Geoffrey Burdett

1,906
1
14
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Javascript get random variables from array but each just once

4 Answers4