Ask a php multi-dimensional array sorting question

Php beginners ask a question. The original array structure is as follows. The original array is sorted by ads_id and time. The current requirement is to re-sort based on the sum of the num of the Two-dimensional array {code ...} the final implementation sorting is as follows: {code ...} ask a new php user a question;
The original array structure is as follows. The original array is sorted by ads_id and time;
Now we need to re-sort the data based on the num Sum of the Two-dimensional array.

Array(    [5] => Array        (            [0] => Array                (                    [num] => 840                    [time] => 2015-10                    [ads_id] => 5                )            [1] => Array                (                    [num] => 684                    [time] => 2015-11                    [ads_id] => 5                )        )    [6] => Array        (            [0] => Array                (                    [num] => 23                    [time] => 2015-10                    [ads_id] => 6                )            [1] => Array                (                    [num] => 37                    [time] => 2015-11                    [ads_id] => 6                )        )    [7] => Array        (            [0] => Array                (                    [num] => 280                    [time] => 2015-10                    [ads_id] => 7                )            [1] => Array                (                    [num] => 343                    [time] => 2015-11                    [ads_id] => 7                )        ))

The sorting is as follows:

Array(    [5] => Array        (            [0] => Array                (                    [num] => 840                    [time] => 2015-10                    [ads_id] => 5                )            [1] => Array                (                    [num] => 684                    [time] => 2015-11                    [ads_id] => 5                )        )            [7] => Array        (            [0] => Array                (                    [num] => 280                    [time] => 2015-10                    [ads_id] => 7                )            [1] => Array                (                    [num] => 343                    [time] => 2015-11                    [ads_id] => 7                )        )            [6] => Array        (            [0] => Array                (                    [num] => 23                    [time] => 2015-10                    [ads_id] => 6                )            [1] => Array                (                    [num] => 37                    [time] => 2015-11                    [ads_id] => 6                )        ))

Reply content:

Ask a new php user a question;
The original array structure is as follows. The original array is sorted by ads_id and time;
Now we need to re-sort the data based on the num Sum of the Two-dimensional array.

Array(    [5] => Array        (            [0] => Array                (                    [num] => 840                    [time] => 2015-10                    [ads_id] => 5                )            [1] => Array                (                    [num] => 684                    [time] => 2015-11                    [ads_id] => 5                )        )    [6] => Array        (            [0] => Array                (                    [num] => 23                    [time] => 2015-10                    [ads_id] => 6                )            [1] => Array                (                    [num] => 37                    [time] => 2015-11                    [ads_id] => 6                )        )    [7] => Array        (            [0] => Array                (                    [num] => 280                    [time] => 2015-10                    [ads_id] => 7                )            [1] => Array                (                    [num] => 343                    [time] => 2015-11                    [ads_id] => 7                )        ))

The sorting is as follows:

Array(    [5] => Array        (            [0] => Array                (                    [num] => 840                    [time] => 2015-10                    [ads_id] => 5                )            [1] => Array                (                    [num] => 684                    [time] => 2015-11                    [ads_id] => 5                )        )            [7] => Array        (            [0] => Array                (                    [num] => 280                    [time] => 2015-10                    [ads_id] => 7                )            [1] => Array                (                    [num] => 343                    [time] => 2015-11                    [ads_id] => 7                )        )            [6] => Array        (            [0] => Array                (                    [num] => 23                    [time] => 2015-10                    [ads_id] => 6                )            [1] => Array                (                    [num] => 37                    [time] => 2015-11                    [ads_id] => 6                )        ))

function mySort($a, $b) {    $sumA = 0;    $sumB = 0;    foreach($a as $ele) {        $sumA += $ele['num'];    }    foreach($b as $ele) {        $sumB += $ele['num'];    }    return $sumB < $sumA;}usort($arr, 'mySort');

UseusortCustom sorting rules