Undefined index when Grouping and sum values in multidimensional array

I am using the below code to group the array $summary by currency and get the sum of grouped duration and cost. So far I am able to group and sum the array but since the array cells $result[$split['currency']]['duration'] and $result[$split['currency']]['cost'] are undefined I am getting notice when I run the code. How can I remove the notice without using error_reporting(0)?

Code

foreach ($summary as $split) {

            if (isset($split['currency'])) {
                $result[$split['currency']]['duration'] += $split['duration'];
                $result[$split['currency']]['cost'] += $split['cost'];
            } else {
                $result[0]['duration'] += $split['duration'];
                $result[0]['cost'] += $split['cost'];
            }
        }

EDIT

$summary = Array
(
[0] => Array
    (
        [currency] => SGD
        [duration] => 8.00
        [cost] => 228.57
    )

[1] => Array
    (
        [currency] => SGD
        [duration] => 8.00
        [cost] => 228.57
    )

[2] => Array
    (
        [currency] => 
        [duration] => 8.00
        [cost] => 
    )

[3] => Array
    (
        [currency] => MYR
        [duration] => 12.00
        [cost] => 342.86
    )

[4] => Array
    (
        [currency] => SGD
        [duration] => 8.00
        [cost] => 228.57
    )

[5] => Array
    (
        [currency] => MYR
        [duration] => 12.00
        [cost] => 342.86
    )

$result will be as show below

 Array
(
[0] => Array
    (
        [currency] => SGD
        [duration] => 24
        [cost] => 685.71
    )

[1] => Array
    (
        [currency] => MYR
        [duration] => 24
        [cost] => 685.72
    )

[2] => Array
    (
        [currency] => 
        [duration] => 8
        [cost] => 0
    )

)

You need to define the array first:

foreach ($summary as $split) {
        if (isset($split['currency'])) {
            if (!isset($result[$split['currency']]) {
                $result[$split['currency']] = [
                    'duration' => 0,
                    'cost' => 0
                ];
            }
            $result[$split['currency']]['duration'] += $split['duration'];
            $result[$split['currency']]['cost'] += $split['cost'];
        } else {
            $result[0]['duration'] += $split['duration'];
            $result[0]['cost'] += $split['cost'];
        }
    }