如何将mysql数组转换为php数组

i have a array like below:

Array ( [0] => stdClass Object ( [city_name] => Hyderabad ) 
        [1] => stdClass Object ( [city_name] => Visakhapatnam )
        [and so on..] => and so on...
      )

this array is return by this block of code:::

 $query = "select city_name from city";
 $result = $CI->Dbmodel->customQueryResult($query);
 print_r(array_values($result));

and i would like to convert the above array to:

array('Hyderabad','Visakhapatnam','and so on..')

do php provide any built-in-function?

how can i do this?.. any help or suggestion would be a great help..thanks in advance

This should work:

$query = "select city_name from city";
$result = $CI->Dbmodel->customQueryResult($query)->result_array();
print_r($result);

If you can't modify your model use this code

$reslt = array();
    foreach($result_array as $value){
        $reslt[] = $value->city_name;
    }

or use result_array() function.