Php apply discount to multiple products evenly - php

Question

Im trying to figure something out. I want to apply coupon/discount amount to multiple products evenly.
For example if I have an array with 3 items
Array
(
[0] => stdClass Object
(
[id] => 1
[price] => 10.00
)
[1] => stdClass Object
(
[id] => 2
[price] => 20.00
)
[2] => stdClass Object
(
[id] => 3
[price] => 30.00
)
)
my coupon vale is 10 $ off
and I have tried this:
foreach ($array as $row) {
$data['price'] = ($row->price - 10 / 3) * 100
}
So basically I want to deduct from each item price proportionally total of 10 and end up with something like:
Array
(
[0] => stdClass Object
(
[id] => 1
[price] => 7.50
)
[1] => stdClass Object
(
[id] => 2
[price] => 17.50
)
[2] => stdClass Object
(
[id] => 3
[price] => 25.00
)
)
where total price sum is 50 instead original of 60

Answer 1

So, from the comments under the question, you want to distribute the coupon value proportionally (not evenly) to prices of all items. That's pretty easy, it's more a mathematical problem than a programming one.
Calculate x as coupon / sum(prices)
Iterate through all items and subtract x * item_price from item_price
That's it.
For your example (coupon = 10, prices = [10, 20, 30]), the result is:
x = 10 / 60 = 0.1666667
Subtract x * item_price from each item's item_price:
10 - 10 * 0.1666667 = 10 - 1.6666667 = 8.33333
20 - 20 * 0.1666667 = 20 - 3.3333333 = 16.6666
30 - 30 * 0.1666667 = 30 - 5 = 25
To verify: 1.666667 + 3.3333333 + 5 = 10