Weighted number generator

NumberGenerator.php

<?php
/**
 * Number generator
 *
 * Generates random numbers with weighting.
 * Pass in an associative array, such as 
 *
 * array(
 *    'A' => 10, // 10% chance
 *    'B' => 30, // 30% chance
 *    'C' => 60 // 60% chance
 * );
 *
 * Values are relative to each other, for example if the weights were 5 and 10, 
 * The value with the weight of 10 is twice as likely to be selected.
 * 
 * Example usage:
 * $generator = new NumberGenerator();
 * $generator->weightedValues = array(
 *     '50% off' => '5', 
 *     '25% off' => '10', 
 *     '20% off' => '15', 
 *     '10% off' => '30',
 *     '5% off' => '40'
 * );
 * echo $generator->getWeightedRandom();
 *
 * @author Ricky Dunlop <[email protected]>
 **/
class NumberGenerator {
    public $weightedValues = array();

    /**
     * Generates a random number which is lower than the sum of the weights
     * Loops through array of weights subtracting the weights from the random number
     * in order until the random number is negative then returns the key
     * 
     * @param array $weightedValues
     */
    public function getWeightedRandom() {
        $rand = mt_rand(1, (int) array_sum($this->weightedValues));

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