Stable sort function

stable_sort.php

/*
 * This file is part of the ICanBoogie package.
 *
 * (c) Olivier Laviale <olivier.laviale@gmail.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace ICanBoogie;

/**
 * Sorts an array using a stable sorting algorithm while preserving its keys.
 *
 * A stable sorting algorithm maintains the relative order of values with equal keys.
 *
 * The array is always sorted in ascending order but one can use the array_reverse() function to
 * reverse the array. Also keys are preserved, even numeric ones, use the array_values() function
 * to create an array with an ascending index.
 *
 * @param array &$array
 * @param callable $picker
 */
function stable_sort(&$array, $picker=null)
{
	static $transform, $restore;

	if (!$transform)
	{
		$transform = function(&$v, $k)
		{
			$v = array($v, $k, $v);
		};

		$restore = function(&$v, $k)
		{
			$v = $v[2];
		};
	}

	if ($picker)
	{
		array_walk
		(
			$array, function(&$v, $k) use ($picker)
			{
				$v = array($picker($v), $k, $v);
			}
		);
	}
	else
	{
		array_walk($array, $transform);
	}

	asort($array);

	array_walk($array, $restore);
}

No documentation on the args for the callable.

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