public static function normalize($list, $assoc = true, $sep = ',', $trim = true) {
		if (is_string($list)) {
			$list = explode($sep, $list);
			$list = ($trim) ? array_map('trim', $list) : $list;
			return ($assoc) ? static::normalize($list) : $list;
		}

		if (!is_array($list)) {
			return $list;
		}

		$keys = array_keys($list);
		$count = count($keys);
		$numeric = true;

		if (!$assoc) {
			for ($i = 0; $i < $count; $i++) {
				if (!is_int($keys[$i])) {
					$numeric = false;
					break;
				}
			}
		}

		if (!$numeric || $assoc) {
			$newList = [];
			for ($i = 0; $i < $count; $i++) {
				if (is_int($keys[$i]) && is_scalar($list[$keys[$i]])) {
					$newList[$list[$keys[$i]]] = null;
				} else {
					$newList[$keys[$i]] = $list[$keys[$i]];
				}
			}
			$list = $newList;
		}
		return $list;
	}