$data=array(
array('text'=>'str1', 'year'=>'2010', 'author'=>10),
array('text'=>'str2', 'year'=>'2011', 'author'=>10),
array('text'=>'str3', 'year'=>'2009', 'author'=>20),
array('text'=>'str4', 'year'=>'2010', 'author'=>30),
array('text'=>'str5', 'year'=>'2010', 'author'=>20),
array('text'=>'str6', 'year'=>'2011', 'author'=>10),
array('text'=>'str7', 'year'=>'2011', 'author'=>20),
array('text'=>'str8', 'year'=>'2009', 'author'=>20),
);
$data_author=array();
foreach($data as $key=>$arr){
$data_author[$key]=$arr['author'];
}
$data_year=array();
foreach($data as $key=>$arr){
$data_year[$key]=$arr['year'];
}
array_multisort($data_year, SORT_NUMERIC, $data_author, $data);
var_export($data);
array(
0 => array('text' => 'str3', 'year' => '2009', 'author' => 20, ),
1 => array('text' => 'str8', 'year' => '2009', 'author' => 20, ),
2 => array('text' => 'str1', 'year' => '2010', 'author' => 10, ),
3 => array('text' => 'str5', 'year' => '2010', 'author' => 20, ),
4 => array('text' => 'str4', 'year' => '2010', 'author' => 30, ),
5 => array('text' => 'str2', 'year' => '2011', 'author' => 10, ),
6 => array('text' => 'str6', 'year' => '2011', 'author' => 10, ),
7 => array('text' => 'str7', 'year' => '2011', 'author' => 20, ),
);