Loop through an array and group prices by month, Morris chart - php

Question

I want to group results by month, to be precise Sum of total prices for each month, but i don't understand how i can divide months, then Sum price for each month.
This is required for morris chart like this
$data2[] = array(
'y' => $month,
'a' => price,
'b' => ''
);
I was using before query to get this results and was a easy way to do it, but now with code is different story.
Any help with explanation of how each segment of code is work will be so nice, so i can avoid problems like this one in future.
I need something like this :
$month = [May, June];
$price = [Sum of all prices for May, Sum of all prices for June];
This is a code :
$monthsArray = array();
// get all dates in array
foreach ($array as $key) {
// convert dates to short format, month-year -> Jun-18
$monthsArray[] = date('M-y', strtotime($key['time']));
}
$months = array();
foreach ($monthsArray as $date) {
$mon = substr($date, 0, 6);
if (!in_array($mon, $months)) array_push($months, $mon);
}
foreach ($months as $m) {
// final array for chart
$data2[] = array('y'=>$m, 'a'=>'', 'b'=>'');
}
$morris = json_encode($data2);
This is array i have
Array
(
[0] => Array
(
[price] => -1835.25
[time] => 2018-05-29 16:53:38
)
[1] => Array
(
[price] => -1743.52
[time] => 2018-05-29 16:53:39
)
[2] => Array
(
[price] => -4445.55
[time] => 2018-05-31 13:21:04
)
[3] => Array
(
[price] => -34647.04
[time] => 2018-05-31 18:29:43
)
[4] => Array
(
[price] => 16888.41
[time] => 2018-06-01 15:05:24
)
[5] => Array
(
[price] => 14369.05
[time] => 2018-06-07 14:44:21
)
[6] => Array
(
[price] => -49579.69
[time] => 2018-06-11 09:14:42
)
[7] => Array
(
[price] => -33300.94
[time] => 2018-06-08 23:50:29
)
[8] => Array
(
[price] => 4413.21
[time] => 2018-06-12 07:15:52
)
[9] => Array
(
[price] => 2724.69
[time] => 2018-06-12 07:15:46
)
[10] => Array
(
[price] => 10224.03
[time] => 2018-06-08 14:00:13
)
[11] => Array
(
[price] => -797.92
[time] => 2018-06-08 13:54:08
)
[12] => Array
(
[price] => -25157.34
[time] => 2018-06-11 11:31:31
)
[13] => Array
(
[price] => 2701.6
[time] => 2018-06-11 14:32:08
)
[14] => Array
(
[price] => 2038.92
[time] => 2018-06-12 07:15:48
)
[15] => Array
(
[price] => -10541.58
[time] => 2018-06-15 10:35:58
)
)
EDIT:
I manage to group months as you can see in updated code and now i am getting only 2 results as i should be, now its just a issue with SUM of data for each month.
This is what i am getting in console
0: {y: "May-18", a: "", b: ""}
1: {y: "Jun-18", a: "", b: ""}