in_array() very slow performance

[JustinK101]

I have the following simple code to test against collision on a primary key I am creating:

 

        $machine_ids = array();
for($i = 0; $i < 100000; $i++) {
	//Generate machine id returns a 15 character alphanumeric string
                $mid = Functions::generate_machine_id();

	if(in_array($mid, $machine_ids)) {
		die("Collision!");
	} else {
		$machine_ids[] = $mid;	
	}
}

die("Success!");

 

Any idea why this is taking minutes to run? Anyway to speed it up?

[gizmola]

Maybe it's because you are generating 100000 15 character strings (using some algorithm you didn't include) and checking that there are no duplicates.

[JustinK101]

The generator algorithm inst the problem, ran the code without the check and under a second. I know I am checking 100,000. That's the entire point. Honestly, 100,000 element array inst that much in today's scale.

[gizmola]

Sorry I don't believe you.  You ran your algorithm 100k times and it ran in 1 second?  I'd like to see some proof of that.

[JustinK101]

Stackoverflow to the rescue, here is the solution, runs in 2 seconds.

 

for($i = 0; $i < 100000; $i++) 
{
  //Generate machine id returns a 15 character alphanumeric string
  $mid = Functions::generate_machine_id();
   if (isset($machine_ids[$mid])) {
       die("Collision!");
   } else {
      $machine_ids[$mid] = true;
   }
}

[JustinK101]

@gizmola

 

Here is the function you wanted to see by the way. No wizardry, just fast.

 

public static function generate_machine_id($length = 15) {
		$password = "";
		$possible = "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

    	$maxlength = strlen($possible);
    	
    	if ($length > $maxlength) {
      		$length = $maxlength;
    	}
    	
    	$i = 0;
    	
    	while ($i < $length) {
     		$password .= substr($possible, mt_rand(0, $maxlength-1), 1);
       		$i++;
    	}
    	
    	return $password;
    }