Divide values from 2 arrays - php

Question

I have this array
$a = [
0 => [
'period' => '2017/2018',
'product' => 'AM',
'quantity_1' => 20,
'quantity' => 25,
],
1 => [
'period' => '2018/2019',
'product' => 'AM',
'quantity_1' => 12,
'quantity' => 19,
],
2 => [
'period' => '2017/2018',
'product' => 'DC',
'quantity_1' => 20,
'quantity' => 25,
],
3 => [
'period' => '2018/2019',
'product' => 'DC',
'quantity_1' => 8,
'quantity' => 10,
]
]
The idea is to divide values by period and by product, in this case we have 2 products 'AM' && 'DC'. So divide values fom 2018/2019 to 2017/2018 for product AM and for product DC. I need to get the result like this :
$result = [
0 => [
'product' => 'AM'
'quantity_1' => 12/20 = 0.6
'quantity_2' => 19/25 = 0.76
],
1 => [
'product' => 'DC'
'quantity_1' => 8/20 = 0.4
'quantity_2' => 10/25 = 0.4
]
]
I tried with foreach but I think exist some other easy ways to do that. If you have some ideas I will appreciate this. Thank you for your time.
I tried like this :
$i = 0;
foreach ($results as $result){
$result[] = [
'product' => $result['product'],
'tonnes_prod' => $results[$i+1]['quantity_1'] / $results[$i]['quantity_1']
];
$i++;
}
But I get the error : #message: "Notice: Undefined offset: 28"

Answer 1

Remake your array first, and then calculate the result
$temp = [];
foreach ($a as $x){
$temp[$x['product']][$x['period']] = $x;
}
$result = [];
foreach ($temp as $key => $res){
$result[] = [
'product' => $key,
'quantity_1' => $res['2018/2019']['quantity_1'] / $res['2017/2018']['quantity_1'],
'quantity_2' => $res['2018/2019']['quantity'] / $res['2017/2018']['quantity'],
];
}
demo