Centrino

$arr_id = [];
foreach ($row as $value) {
       if (isset($arr_id[$value['id']])) {
                $arr_id[$value['id']]  += $value['num'];
                continue;
       }
       $arr_id[$value['id']] = $value['num'];
}
$row = [];
foreach ( $arr_id as $key => $value) {
        $row[] = [
                'id' => $key;
                'num' => $value;
        ];
}