Shuffling array, without shuffle()

[Anon]

Hi,

How can I shuffle an array (randomize its elements) without using shuffle() function - it's not supported on my ISP for whatever reason.

I'm getting an array of 'image links' from MySQL table. I thought I could use 'ORDER BY RAND() LIMIT 100' in my query, but it's possible only with v. 3.23, which my ISP doesn't support either :-(

I'm using PHP 4.

Thank you,

Alex

[Anon]

Could you perhaps asign a number to each element and then use rand?

Nick

[saloon12yrd]

my approach would be:
0) create an empty array $nums
1) count() the original arrays size
2) for-loop around this number
3) generate a rand() number $n from 0 to count()-1
4) check whether $n is already in_array(array_keys($nums)), if no store $n in $nums, if yes use the last/first element from the original array
5) remove the $n'th element from the original array
6) end for loop

With that you'd end up in a shuffled copy of the original. Note that this is a rather greedy approach, you might end up in timing issues on really large arrays.

Greets,

Dominique

[[deleted]]

Small optimization to that idea;
You could just loop through every element and swap it with a random element.

srand ((double) microtime() * 1000000);
$aArray=array(1,2,3,4,5,6,7,8,9,0);
echo '<pre>';
print_r($aArray);
for ($t=0;$t<count($aArray);$t++)
{
$iRandVal = rand(0,count($aArray)-1);
$mTemp = $aArray[$iRandVal];
$aArray[$iRandVal]=$aArray[$t];
$aArray[$t]=$mTemp;
};
print_r($aArray);
echo '</pre>';

[Anon]

Thank you, guys.
Here is yet another solution I came up with:

<xmp>

function shuffle_array ($arr) {

    //returns randomized-shuffled array
    $new_arr = array(); //empty array
    $num = count($arr);

    srand(time());

    for ($i=0; $i<$num; ++$i) {

        $pos = rand(0, count($arr)-1);
        array_push($new_arr, $arr[$pos]);

        unset($arr[$pos]); //destroy element

    }

    return $new_arr;

}

</xmp>

It shuffles OK, but I'm not sure if some elements are lost along the way.

Alex

[[deleted]]

Clever, quite clever.

Now it's down to benchmarking to see which method is fastest :-)