Вывод только уникальных значений свойств

$arSelect = Array("ID", "NAME", "PREVIEW_TEXT","PREVIEW_PICTURE", "PROPERTY_BRAND","DETAIL_PAGE_URL");
$arFilter = Array("IBLOCK_ID"=>5, "ACTIVE"=>"Y");
$arGroupBy=Array("PROPERTY_BRAND");
$db_list = CIBlockElement::GetList(Array("NAME"=>"ASC"), $arFilter, $arGroupBy, false, $arSelect);
while($ar_result = $db_list->GetNext())
{

}