Как разбить значения доп.полей и удалить повторения?

if(!$xflist) {
	$sql_result = $db->query( "SELECT xfields FROM " . PREFIX . "_post WHERE approve=1" );
	while ( $rows = $db->get_row( $sql_result ) ) {
		$xfields[] = $rows;
	}
	$stack = array();
	foreach($xfields as $value){
		if($value[xfields]){
			$row = xfieldsdataload($value[xfields]);
			if($row[$xfname]){
				$rowdata = explode( "~", $row[$xfname]);
				foreach($rowdata as $value){
					if($value){
						$value = trim($value);
						array_unshift($stack, $value);
					}
				}
			}
		}
	}
	$stack = array_unique($stack);
	sort ($stack);	
	foreach($stack as $value){
		$vala = explode(",", $value);
		foreach ($vala as $valka) {
			$xflist .= "<option value=" . $valka . ">" . $valka . "</option>";
		}
	}
	create_cache($xfname, $xflist, $config['skin']);
}