I've searched through some of the answers here but it doesn't seem the thing that I needed or I just don't know how to apply it though.

I haven't started any codes and I'm only thinking on how to do it and I have no idea how to do it. I need your help guys.

Let's assume that I have an array which consists of these values below

[1,2,3,4,5,6,7,8,9]

And I need to shuffle it without repeating the position of each numbers of the last result. so it would probably like

[5,3,9,6,2,8,1,4,7]

if I shuffle it again it would be like

[4,7,2,1,8,3,6,9,5]

And so on.

Well I don't know if there' any relevance to it but, would rather not to use rand() though. Any solution for this stuff?

I've searched through some of the answers here but it doesn't seem the thing that I needed or I just don't know how to apply it though.

I haven't started any codes and I'm only thinking on how to do it and I have no idea how to do it. I need your help guys.

Let's assume that I have an array which consists of these values below

[1,2,3,4,5,6,7,8,9]

And I need to shuffle it without repeating the position of each numbers of the last result. so it would probably like

[5,3,9,6,2,8,1,4,7]

if I shuffle it again it would be like

[4,7,2,1,8,3,6,9,5]

And so on.

Well I don't know if there' any relevance to it but, would rather not to use rand() though. Any solution for this stuff?

• php
• javascript
• arrays
• shuffle

• Do you want to create every possible bination? If not just shuffle the array, pare it to each of the already shuffled arrays. if it matches reshuffle it, if not add it. – Imperative Commented Feb 21, 2013 at 13:47
• 1 In php you can use function shuffle(&$array). Pass an array - and it will shuffle it for you. You can't guarantee constant non-repeat, but you're very-very unlikely to get repeated results on two subsequent calls. – Aleks G Commented Feb 21, 2013 at 13:48
• you can also split the array into smaller array, shuffle those, and recreate the large array from the smaller arrays in a random order. So you end up with [2,3,1][6,5,4][8,9,7] and then maybe [6,5,4][2,3,1][8,9,7] which when merged bees : [6,5,4,2,3,1,8,9,7] – Husman Commented Feb 21, 2013 at 13:51
• so you don't want the numbers to repeat in the same position for how many iterations/suffles? – Hugo Alves Commented Feb 21, 2013 at 13:56
• @Bergi from what i understand he doesn't what each number to repeat the same/last position where it was for n suffles. so it's not a duplicate – Hugo Alves Commented Feb 21, 2013 at 13:59

6 Answers 6

Try this,

$count = 15;
$values = range(1, $count);
shuffle($values);
$values = array_slice($values, 0, 15);

OR

$numbers = array();
do {
   $possible = rand(1,15);
   if (!isset($numbers[$possible])) {
      $numbers[$possible] = true;
   }
} while (count($numbers) < 15);
print_r(array_keys($numbers));

may this help you.

What you want to do is to add elements from your array to another array, randomly, but to ensure that elements are not in the same indexed position. Try this:

$array = [1,2,3,4,5,6,7,8,9];
$new = array();
for($i = 0; $i < $array.length; $i++){
  $rand = $i;
  do {
    $rand = Math.floor( Math.random() * ( $array.length + 1 ) );
  } while ($rand == $i || array_key_exists($rand, $new))
  // Check that new position is not equal to current index
  // and that it doesnt contain another element

  $new[$rand] = $array[i];
}

Not the most efficient, but guaranteed to put elements in non same indices.

You can use the variant of the Fisher-Yates-Shuffle which does biased randomly choose the swapped element and is known as Sattolo's algorithm:

function shuffleArray(array) {
    for (var i = array.length - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * i); // no +1 here!
        var temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
    return array;
}

That way, every element is guaranteed to be swapped and not appear in the same position as before.

This makes the values of the array not repeat any previous position for n shuffles (i'm using half of the array's size as n, after that i restart the forbidden indexes). At the end a modified this version to make it not repeat the current position.

For this you will have to save a history of all the index where each value of the orignal array has been. To do this i've added a little more plexity to your numbers

var numberArray = [{value:1, unavailable_indexes:[0]},
                   {value:2, unavailable_indexes:[1]},
                   {value:3, unavailable_indexes:[2]},
                   {value:4, unavailable_indexes:[3]},
                   {value:5, unavailable_indexes:[4]},
                   {value:6, unavailable_indexes:[5]},
                   {value:7, unavailable_indexes:[6]},
                   {value:8, unavailable_indexes:[7]},
                   {value:9, unavailable_indexes:[8]}
                  ];

this way you have the number in value and an array of all the positions where it has been. Next we need to run all the array and switch numbers around.

var arrayLen = numberArray.length-1;
$.each(numberArray, function(index, value){
    var newIndex;
    //restart the array when half of the index have been covered or it will take awhile to get a random index that wasn't used
    if(value.unavailable_indexes.length >= numberArray.length/2)
        value.unavailable_indexes = [index];//restart the unavailable indexes with the current index as unavailable
    do{
        newIndex = Math.floor(Math.random()*arrayLen);
    //verify if you can swap the 2 values, if any of them have been on the destination index get another random index
    }while($.inArray(value.unavailable_indexes, newIndex) || $.inArray(numberArray[newIndex].unavailable_indexes, index));


    numberArray[index] = numberArray[newIndex];
    numberArray[newIndex] = value;
})

after all the array has been moved around you need to save the positions where they landed

$.each(numberArray, function(index, value){
   value.unavailable_indexes.push(index);
}

EDIT: if you just want to prevent it from just repeating the previous position then make unavailable_indexes hold the last position it was in and replace the do{...}while() with:

do{
    newIndex = Math.floor(Math.random()*arrayLen);
}while(newIndex != value.unavailable_indexes)

and the last method would look like:

$.each(numberArray, function(index, value){
   value.unavailable_indexes = index;
}

I just came up with the following code, to bat a problem I was having where sometimes my randomly shuffled array would end up in it's original order (was it too random, or not random enough?).

How it works, it loops over a while loop until the $isDifferent variable bees true, which can only happen if the arrays do not match. This perhaps may work similarly to the Fisher-Yates method, although when I tried that, I still ended up with matching arrays on occasion.

This solution is written in PHP but could easily be converted to JavaScript.

guaranteedShuffle($array){
    $isDifferent = false;
    while(!$isDifferent){
        $arrayCopy = $array;
        shuffle($arrayCopy);
        if($array !== $arrayCopy){
            $isDifferent = true;
        }
    }
    return $arrayCopy;
} 

Usage:

$array = ['1','2']; 
$shuffled = guaranteedShuffle($array);

You can shuffle using Fisher Yates Shuffle

function fisherYates ( myArray ) {
var i = myArray.length, j, tempi, tempj;
if ( i == 0 ) return false;
while ( --i ) {
 j = Math.floor( Math.random() * ( i + 1 ) );
 tempi = myArray[i];
 tempj = myArray[j];
 myArray[i] = tempj;
 myArray[j] = tempi;
}
}

See this reference