// $arResult["ITEMS"] - многомерный массив произвольного уровня вложенности
$sort_numcie = array();
foreach($arResult["ITEMS"] as $val) {
    $sort_numcie[] = $val['SORT'];
}
array_multisort($sort_numcie, SORT_ASC, $arResult["ITEMS"]); // false

$sort_numcie = array();
foreach($arResult["ITEMS"] as $key => $val) {
    $sort_numcie[$key] = $val['SORT'];
}
array_multisort($sort_numcie, SORT_ASC, $arResult["ITEMS"]);

$ar = array(
       array("10", 11, 100, 100, "a"),
       array(   1,  2, "2",   3,   1)
      );
array_multisort($ar[0], SORT_ASC, SORT_STRING,
                $ar[1], SORT_NUMERIC, SORT_DESC);

$price = array();
foreach ($inventory as $key => $row)
{
    $price[$key] = $row['price'];
}

array_multisort($price, SORT_DESC, $inventory);