Biased Random Value From Array With PHP

10th March 2008 - 2 minutes read time

Sometimes you will want to get a random value form an array in a biased random way, that is, you will want certain values to be returned more than others. Here is a function that will generate a single key from an array, with a greater change of a higher value being retrieved.

function biasedRandom($numbers){
 $total = 0;
 foreach($numbers as $number=>$weight){
  $total += $weight;
  $distribution[$number] = $total;
 $rand = mt_rand(0,$total-1);
 foreach($distribution as $number=>$weights){
   return $number;

This function is used in the following way.

//set up array
$array = array('one'=>100,
// get biased random number
echo biasedRandom($array);

The key that is generated the most by the function is four because it has a higher value than the rest and will therefore 'weigh' a lot more.

Add new comment

The content of this field is kept private and will not be shown publicly.