<?php

/**
 * sort_multi_array
 *
 * Sort a two-dimensional array by one (or more) of the elements in the nested arrays. Accepts a variable number of arguments.
 *
 * @version 0.1
 * @author Contributors at eXorithm
 * @link /algorithm/view/sort_multi_array Listing at eXorithm
 * @link /algorithm/history/sort_multi_array History at eXorithm
 * @license /home/show/license
 *
 * @param array $array Two dimensional array. Each array in the array should have the same keys.
 * @param mixed $key Key in the sub-arrays to sort by.
 * @return array
 */
function sort_multi_array($array=array(0=>array('surname'=>'Smith','givenname'=>'Henrietta'),1=>array('surname'=>'Smythe','givenname'=>'Stuart'),2=>array('surname'=>'Black','givenname'=>'Conrad'),3=>array('surname'=>'Smith','givenname'=>'Abigail'),4=>array('surname'=>'Eaves','givenname'=>'Ruth'),5=>array('surname'=>'Travis','givenname'=>'Earl')),$key='surname')
{
	$keys = array();
	for ($i=1;$i<func_num_args();$i++) {
		$keys[$i-1] = func_get_arg($i);
	}
	
	// create a custom search function to pass to usort
	$func = function ($a, $b) use ($keys) {
		for ($i=0;$i<count($keys);$i++) {
			if ($a[$keys[$i]] != $b[$keys[$i]]) {
				return ($a[$keys[$i]] < $b[$keys[$i]]) ? -1 : 1;
			}
		}
		return 0;
	};
	
	usort($array, $func);
	
	return $array;
}

?>

<?php

/**
 * hailstone
 *
 * Calculates a hailstone sequence.
http://en.wikipedia.org/wiki/Collatz_conjecture
 *
 * @version 0.3
 * @author Contributors at eXorithm
 * @link /algorithm/view/hailstone Listing at eXorithm
 * @link /algorithm/history/hailstone History at eXorithm
 * @license /home/show/license
 *
 * @param number $number number to start with
 * @return array
 */
function hailstone($number=17)
{
	$result = array();
	
	while ($number > 1) {
		$result[] = $number;
		if ($number & 1)
			$number = 3 * $number + 1;
		else
			$number = $number / 2;
	}
	
	$result[] = $number;
	
	return $result;
}

?>