generating non-repeating random numbers from a range

[lli2k5]

Is there a function in PHP to do this? Or would it have to be created?

[Weedpacket]

Why ask? Why not browse through the manual and find [man]array_rand[/man] for yourself?

[lli2k5]

I'm trying to allow for no repeats.

[KevinMG]

I believe this should do it...

<?php
function nonRepeat($min,$max,$count) {

//prevent function from hanging 
//due to a request of more values than are possible	
if($max - $min < $count) {
	return false;
}

   $nonrepeatarray = array();
   for($i = 0; $i < $count; $i++) {
      $rand = rand($min,$max);

  //ensure value isn't already in the array
  //if it is, recalculate the rand until we
  //find one that's not in the array
  while(in_array($rand,$nonrepeatarray)) {
	$rand = rand($min,$max);
  }

  //add it to the array
  $nonrepeatarray[$i] = $rand;
   }
   return $nonrepeatarray;
}


//give it a test run
$test = nonRepeat(0,20,20);
echo "<pre>";
print_r($test);
echo "</pre>";
?>

[lli2k5]

it works man

[Installer]

That'll work fine for smaller arrays, but for very large ones, with $count also large, it could get really slow. This version will avoid that, while also not having to stumble on frequent duplicates:

function non_repeat($min, $max, $count)
{
    if ($max - $min < $count) { 
        return false; 
    } 
    $arr = range($min, $max);
    shuffle($arr);
    $nonrepeatarray = array_slice($arr, 0, $count);
    return $nonrepeatarray;
}

[Weedpacket]

To avoid repeats you can also use [man]array_rand[/man].... I did mention array_rand at some stage didn't I?

[Installer]

An array_rand() version:

function non_repeat($min, $max, $count, $sort = false) 
{ 
    if ($max - $min < $count) { 
        return false; 
    } 
    $arr = range($min, $max);
    $arr_rnd = array_rand($arr, $count);
    foreach ($arr_rnd as $each) {
        $nonrepeatarray[] = $arr[$each];
    } 
    if (!$sort) {    

        shuffle($nonrepeatarray);
    }
    return $nonrepeatarray; 
} 

$test = non_repeat(16, 32, 8); 
echo '<pre>'; 
print_r($test); 
echo '</pre>';

[Weedpacket]

Oh, that's overcomplicated 🙂

function sample($min,$max,$count)
{
	// Trivial cases
	if($count>$max-$min+1) return false; // unsatisfiable
	if($count<=0) return array();
	if($min==$max) return array($min);
	if($count==1) return array(mt_rand($min,$max));

return array_rand(array_flip(range($min,$max)), $count);
}

But this is assuming much more about the problem than was given in the question. For all it said the following might have been what was wanted:

function no_repeats($source=null)
{
	static $reserve = null;
	static $backup = null;
	if(is_array($source))
	{
		$backup = $reserve = $source;
		shuffle($reserve);
		return;
	}
	if(count($reserve)==0)
	{
		$reserve = $backup;
		shuffle($reserve);
	}
	return array_shift($reserve);
}


no_repeats(range(1,100));
for($i=0; $i<20; $i++)
    echo no_repeats(),' ';

[Installer]

I couldn't figure out how to use array_flip() for this, and the count-checking is needed even if it wasn't originally asked for. As well, the one-liner style does save code storage space. Thanks for showing us that.

Quoting myself:

An array_rand() version

🙂

[Weedpacket]

Well yeah; obviously there are an infinite number of solutions, both with and without using array_rand(). I think my main beef was reading this

I'm trying to allow for no repeats.

as though array_rand didn't help with that.