random array function

Anon

has anyone ever made up a function that will go thru & randomize multiple arrays ? i have a bunch of arrays i need to randomize...i have smething working but it is so inefficient & hardcoded 14 times. like so:

// INCORRECT answer 1
$q1ans1_list = array ("gravity", "earth's magnetic field", "northern lights");
// seed the random generator.
srand (mktime ());
$q1ans1_list_length = sizeof($q1ans1_list);
$q1ans1_index = (rand() % $q1ans1_list_length);
$q1ans1_text = $q1ans1_list[$q1ans1_index];
$q1ans1_wrong = "studying the source of $q1ans1_text";

so i'm trying to make a function that will loop thru the arrays, pic 1 at random & then combine into the final "$q1ans1_wrong" string at the end. any ideas or pre-built code y'all may have seen ? i am trying something with array_rand() that may be better w/ regard to "srand ((double) microtime() * 10000000);
"...http://www.php.net/manual/en/function.array-rand.php

thanks for any input...
geoff

dstockto

Use the shuffle() command.

http://www.php.net/manual/en/function.shuffle.php

It's whole purpose is randomize the order of the elements in an array.

Dave

Anon

thanks David ! i will check out the shuffle deal...

Anon

wooo, this looks like it might work for me, found it on the shuffle page:

function array_rand_elim (&$array1, $array2 = array ())
{
if (!count ($array1))
return array ();

srand ((double) microtime() * 10000000);
$rand = array_rand ($array1);

$array2[] = $array1[$rand];
unset ($array1[$rand]);

return $array2 + array_rand_elim ($array1, $array2);
}

$array = array_rand_elim ($array);

many of these guys are saying shuffle doesn't work all that great compared to srand(); especially on solaris (where this will eventually live)...the randomness needs to be right on. thanks again -- geoff

dstockto

srand() is just the random number generator seeding function.

What it means is that if you use
srand ((double) microtime() * 1000000);
shuffle($myarray);

You should get a pretty randomized array. Looking at the comments though, this didn't seem to be the case.

The important thing to realize about computer generated random numbers is that they are not really random.

If you make two identical arrays, and call srand(4); (or some other constant) in front of the shuffle for each of the arrays, you should (unless shuffle does weird things) get exactly the same shuffling results in both arrays.

The reason seeding with the microtime works is that since the microseconds are changing so quickly you are pretty certain to get a different seed each time. This would lead to a different sequence of random numbers (*), and thus a different sorted pattern.

(*) Well-written random number generators will loop through x numbers without ever repeating a number until the whole range of numbers has been exhausted. However, they can only produce one loop of numbers. The seed only determines where in the loop of numbers they start reading from. A 32-bit random number generator should be able to produce 2.1 billion (rounded) numbers before starting with the same sequence it began with.