You can either use a 'foreach' block, iterate over each element in your array and sum up its 'rating' value

    foreach($array->items as $item) {
    $sum+=(int)$item->rating;            
    } 
    $result = $sum/5;

Or you can use the array_sum() method

    $sum =array_sum((int)$array->rating);
    $result = $sum/5;

PHP 7 solution:

$result = array_sum(array_column($array_of_objects, 'rating')) / 5;

you can use this code for sum array value using php . First assign variable shich store all sum value so this must set 0 and use loop for make all value sum. this is your code which help you and if your array $your_array then

$sum = 0; // this is store all sum value so first assign 0
foreach ($your_array as $rating)  {          
{
   $sum += $rating->rating; // sum value with previous value and store it and no need to convert string type to int cause php do it 
}
echo $sum; // this is final value
echo $total_sum = $sum / 5; // this is your desire result 

and if your array is associative then use this code

$sum = 0; // this is store all sum value so first assign 0
foreach ($your_array as $rating)  {          
{
   $sum += $rating['rating']; // sum value with previous value and store it and no need to convert string type to int cause php do it 
}
echo $sum; // this is final value
echo $total_sum = $sum / 5; // this is your desire result 

check this code and hope it will help you .