grouping function

groupBy.php

<?php

/**
 * Group an array using a callback or each element's property/index
 *
 * @param array $arr array to group
 * @param callable|string $grouper hashing function, or property/index of each item to group by
 * @return array grouped
 */
function groupBy(array $arr, $grouper)
{
	$first_el = reset($arr);
	$is_array = is_array($first_el) || ($first_el instanceof ArrayAccess);

	// get real grouper func
	$func = is_callable($grouper) ? $grouper : function($x) use ($is_array, $grouper) {
		if ($is_array) {
			return $x[$grouper];
		} else {
			return $x->$grouper;
		}
	};

	$grouped = [];

	foreach ($arr as $item) {
		$hash = $func($item);
		if (!isset($grouped[$hash])) {
			$grouped[$hash] = [];
		}

		$grouped[$hash][] = $item;
	}

	return $grouped;
}