randomizing arrays

drag0n

right now I am using this method of randomizing arrays:

  for ($b = 0; $b < sizeof($possibles); $b++) 
            { 
                $r1 = rand(1,sizeof($possibles)) - 1; 
                $r2 = rand(1,sizeof($possibles)) - 1; 

            $temp = $possibles[$r1]; 
            $possibles[$r1] = $possibles[$r2]; 
            $possibles[$r2] = $temp; 

            $temp = $wid[$r1]; 
            $wid[$r1] = $wid[$r2]; 
            $wid[$r2] = $temp; 
        }

Are there any better ways? My way is a manuel way of just switching arround each array till they are all random... but there must be a function or something?

barand

[man]array_rand[/man]

hth

drag0n

i tried to use that, but somehow it kept spitting out the same stuff or different stuff in same order

drag0n

and also, the $wid and $possibles won't match each other anymore if I randomize them, I am able to get the random wids but then the $possibles arent matching it ...
how do I match them still?

drag0n

hmm what could this be?

swr

array_rand will pull a random item from an array, but you will get some duplicates and some will not be pulled because it is completely random.

If you want to shuffle your array, use [man]shuffle[/man]. It will work better than your function.

drag0n

same problem occurs, the $wid does not match the $possibles anymore 🙁

laserlight

Maybe it would be better if you explain what you are trying to do.

Especially without comments, it is difficult to see what in the world is $possibles and $wid

barand

Have a 3rd array containing 0 , 1, 2 .... up to count(possibles)-1.

Shuffle this third array and use its values as keys to access the other 2 arrays.

Alternatively, put possibles and wids in a 2 dim array and shuffle that.

drag0n

Ok.. What I am trying to do is display a "Quote" which is contained in $possibles in Option Form and have the value of each "Quote" be related to its id which is contained in $wid.
If I shuffle one, the other is not syndicated anymore, so the only way I did it was to the old "switcharoo" trick, but it is not "really" random, so I wanted to use a php func such as rand or shuffle and not messup the sequencing, would it be possible?

barand

Yes - see my previous post

laserlight

Is it possible to make the values in $wid become the keys in $possibles, such that we are dealing with associative arrays?
I'm not too clear on how shuffle() works with associative arrays though.

Another way might be to take advantage of pseudorandom numbers, but then shuffle() is automatically seeded, so it may not work.
This solution involves generating a reasonably random seed, and recording it.
Then use this seed in srand().
After using shuffle() on $possibles, use the seed on srand() again.
Then shuffle() $wid.
Since the same seed should produce the same pseudorandom number sequence, the 2 arrays should be shuffled identically.

drag0n

would the 2 dim arrays work better?

laserlight

For hack value, I'd try out playing with the seed.

For practical purposes, you might as well go with the 2d array as barand suggested.

drag0n

im a bit confused about the seed function, could you show me an example plz?
thanks!

drawmack

I went to google and typed in array shuffling algorithms and the third link on the list was this one:
http://www.zend.com/codex.php?id=578&single=1

This class contains this function:

  /****************************************************************** 
  * 
  * shuffleArray - shuffle the contents of an array. 
  * 
  * snatched from: [url]http://www.zend.com/codex.php?id=10&single=1[/url] 
  * 
  ******************************************************************/ 
  //Use &$array to avoid stack explosion. 
  //PHP4 probably needs something slightly different 
  //since it has true references & counting. 
  function shuffleArray(&$array) 
  { 
    //Assumes array is 0-based integer keys 
    //Initialize the random number generator once, and only once, 
    //Even if we call shuffle function twice in one script. 

if (!isset($randinit)){ 
  srand((double) microtime() * 1000000); 
  static $randinit = 1; 
} 

//Start at the end and work our way forward, 
//always swapping a randomly selected item 
//with the current 'last' one. 
$last = count($array); 
while ($last > 1){ 

  //Earlier versions of PHP had different args for rand(). 
  $random = rand(0, $last); 

  //Swap the randomly selected element with the last element. 
  $temp = $array[$random]; 
  $array[$random] = $array[$last]; 
  $array[$last] = $temp; 

  //Move 'forward' in array 
  $last--; 
} 
return 1; 
  } //shuffleArray

I love google.

drag0n

too bad thats what I was doing before, as you can see from my 1st post 🙂

drawmack

hey neat using 2 arrays = using 1 array as a reference to save on name space I'll have to remember that.

drag0n

yah, i know its a bit mesed up thats why I wanted to really randomize it and not to just do the switcharoo

swr

drag0n,

That's not what you were doing before. What you were doing before was taking a random index and swapping it with another random index, n times. The problem with that is that on average, sqrt(n) items will not be moved at all. The proper algorithm is to go through each index sequentially and swap it with a random index. That gives perfectly random shuffling by ensuring that every element is shuffled at least once.

Untested code:

foreach (array_keys($items) as $i) {
    $j = array_rand($items); // gets a random key
    // Here, swap $items[$i] and $items[$j].
    // Since you have more than one array, also
    // swap $moreitems[$i] and $moreitems[$j].
}