Subtract row values in Array2 from specific row values in Array1 - php

Question

I would like to subtract the quantity of $array2 from the stocks of $array1.
$array1= ([product_id]=>4, [stocks]=>20)
$array2= ([product_id]=>4, [quantity]=>3)
So that would be:
$array1= ([0]=> 4, [1] => 20);
$array2= ([0]=> 4, [1] => 3);
And then the output should be:
$array1= ([0]=> 4, [1] => 17);

Answer 1

Your array structure looks slightly different with multiple records, the code works out like this in an ugly manner. I'm assuming you're talking about something like this:
$array1 = array(
0=>array('product_id'=>4, 'stocks'=>20),
1=>array('product_id'=>5, 'stocks'=>60));
$array2 = array(
0=>array('product_id'=>4, 'quantity'=>3)
1=>array('product_id'=>5, 'quantity'=>30));
...It's a multi-dimensional array (typical for records pulled from a database).
foreach($array1 as $key=>$value){
foreach($array2 as $key2=>$value2) {
if($value['product_id']==$value2['product_id']){
$value['stocks'] -= $value2['quantity'];
//optimization to avoid searching this again.
unset($array2[$key]);
}
}}

Answer 2

With what you have given the following will do what you are asking for:
if($array1['product_id'] == $array2['product_id']) {
$array1['stocks'] -= $array2['quantity'];
}
If you need to loop through a bigger array then what I have given is only part of the larger puzzle.

Answer 3

Jesse's answer wasn't tested and will not provide the desired output because the "stocks" array wasn't being modified -- a copy of the array was being modified in the loop -- so if you try to print the result to screen, there would be no change.
To modify by reference, use & just before the value variable in the first loop.
Also the unset() key must come from the inner loop to be accurate.
Additionally, if the "sales" "product_id"s are unique, then breaking the inner loop upon matching will improve performance. (This is how array_search() works.)
Code: (Demo)
$stocks = [
['product_id'=>2, 'stocks'=>50],
['product_id'=>3, 'stocks'=>100],
['product_id'=>4, 'stocks'=>20],
['product_id'=>5, 'stocks'=>60]
];
$sales = [
['product_id'=>4, 'quantity'=>3],
['product_id'=>5, 'quantity'=>30]
];
foreach ($stocks as &$row) { // modify by reference
foreach ($sales as $k => $row2) { // search for product_id match
if ($row['product_id'] == $row2['product_id']) {
$row['stocks'] -= $row2['quantity']; // subtract
unset($sales[$k]); // eliminate match from lookup array
break; // assuming $sales['product_id'] values are unique
}
}
}
var_export($stocks);
Output:
array (
0 =>
array (
'product_id' => 2,
'stocks' => 50,
),
1 =>
array (
'product_id' => 3,
'stocks' => 100,
),
2 =>
array (
'product_id' => 4,
'stocks' => 17,
),
3 =>
array (
'product_id' => 5,
'stocks' => 30,
),
)
Alternatively, you can converted the sales array into a flattened, product_id-keyed array to serve as a lookup.
Code: (Demo)
$keyed = array_column($sales, 'quantity', 'product_id');
var_export($keyed);
echo "\n---\n";
foreach ($stocks as &$row) { // modify by reference
if (isset($keyed[$row['product_id']])) { // search for product_id match
$row['stocks'] -= $keyed[$row['product_id']]; // subtract
}
}
var_export($stocks);
Output:
array (
4 => 3,
5 => 30,
)
---
array (
0 =>
array (
'product_id' => 2,
'stocks' => 50,
),
1 =>
array (
'product_id' => 3,
'stocks' => 100,
),
2 =>
array (
'product_id' => 4,
'stocks' => 17,
),
3 =>
array (
'product_id' => 5,
'stocks' => 30,
),
)