All About Random Stuff

random_weight

<?php

/**
 * getRandomWeightedElement()
 * Utility function for getting random values with weighting.
 * Pass in an associative array, such as array('A'=>5, 'B'=>45, 'C'=>50)
 * An array like this means that "A" has a 5% chance of being selected, "B" 45%, and "C" 50%.
 * The return value is the array key, A, B, or C in this case.  Note that the values assigned
 * do not have to be percentages.  The values are simply relative to each other.  If one value
 * weight was 2, and the other weight of 1, the value with the weight of 2 has about a 66%
 * chance of being selected.  Also note that weights should be integers.
 *
 * From: http://stackoverflow.com/questions/445235/generating-random-results-by-weight-in-php 
 * @param array $weightedValues
 */
function getRandomWeightedElement(array $weightedValues) {
  $rand = mt_rand(1, (int) array_sum($weightedValues));

  foreach ($weightedValues as $key => $value) {
    $rand -= $value;
    if ($rand <= 0) {
      return $key;
    }
  }
}