php array manipulating keys

Question

I fetched an array from a table

 arr1 = Array
(
    [0] => Array
        (
            [option_value_id] => 30
            [duration_id] => 1
            [price_value] => 13
        )

    [1] => Array
        (
            [option_value_id] => 30
            [duration_id] => 2

            [price_value] => 14
        )

    [2] => Array
        (
            [option_value_id] => 30
            [duration_id] =>3
           [price_value] =>15
 )
[4] => Array
        (


            [option_value_id] => 31
            [duration_id] => 1
            [price_value] => 16

        )

    [5] => Array
        (


            [option_value_id] => 31
            [duration_id] => 2
            [price_value] => 17
        )

    [6] => Array
        (

            [option_value_id] => 31
            [duration_id] =>3
            [price_value] => 18
 )

I need the duration_id as key and option_value_id as key in the duration_id array my resultant array should look like this

Array
    (
        [1] => Array
            (
                [30] => 13
                [31] => 16
            )

        [2] => Array
            (
                [30] => 14
                [31] => 17
            )

        [3] => Array
            (
                [30] => 15
                [31] => 18
            )
)

?>

Answer 1

This should do the trick:

$result = array();
foreach($arr1 as $val){
    $result[$val['duration_id']][$val['option_value_id']] = $val['price_value'];
}