Remove duplicate record in multi dimensional array

<?
error_reporting(1);
$arr1=Array(
    459 => Array
        (
            "maxScore" => 1.7873402,
            "score" => 1.3271129,
            "book_id" => 260,
            "book_part_autoid" => 4161,         
        ),460=> Array(
            "maxScore" => 1.7873402,
            "score" => 1.3268949,
            "book_id" => 260,
            "book_part_autoid" => 4161,           
        ),

    461 => Array
        (
            "maxScore" => 1.7873402,
            "score" => 1.3268949,
            "book_id" => 260,
            "book_part_autoid" => 4164,

        ),462 => Array
        (
            "maxScore" => 1.7873402,
            "score" => 1.32654,
            "book_id" => 260,
            "book_part_autoid" => 4198,
           
        )

);



foreach($arr1 as $key=>$val)
{

         if(!isset($result[$val['book_part_autoid']]))
{
               $result[$val['book_part_autoid']]=$val;

}


}


echo "<pre>";
print_r($result);
echo "</pre>";

?>