PHP在foreach中更改数组值

Question

im quite new to php and as i was looking for info for last 2 hours, no examples seemed to help. i have what i think is called nested array? two of them. pretty much i need to be able to match id from different arrays. and detract the amount from stock.

<?php
$items = array(
array('id' => 34, 'name' => 'Kompiuterius ASUS ASX89', 'price' => 639.00, 'stock' => 3),
array('id' => 1008, 'name' => 'Monitorius AOC 27IPS', 'price' => 223.00, 'stock' => 7),
array('id' => 965, 'name' => 'Tracer kilimėlis pelytei', 'price' => 2.00, 'stock' => 20),
array('id' => 567, 'name' => 'Pelytė Logitech A52', 'price' => 16.00, 'stock' => 14),
array('id' => 1123, 'name' => 'Klaviatūra Razer Chroma 2016', 'price' => 109.00, 'stock' => 6)
);
$orders = array(
array('purchase_date' => '2016-11-12', 'item_id' => 34, 'quantity' => 1),
array('purchase_date' => '2016-11-12', 'item_id' => 1008, 'quantity' => 2),
array('purchase_date' => '2016-11-13', 'item_id' => 965, 'quantity' => 1),
array('purchase_date' => '2016-11-15', 'item_id' => 1123, 'quantity' => 4),
array('purchase_date' => '2016-11-11', 'item_id' => 34, 'quantity' => 2)
);

foreach ($orders as $order){
  $purchase_id = $order['item_id'];
  $purchase_quantity = $order['quantity'];
  foreach ($items as $item){
    $stock_id = $item['id'];
    $stock_quantity = $item['stock'];
    if ($purchase_id == $stock_id){
      $stock_quantity = $stock_quantity - $purchase_quantity;
      $item['stock'] = $stock_quantity; //something with &?
      echo 'Prekiu, pazymetu numeriu ' . $stock_id . ' liko: ' . $stock_quantity . ' vnt. ' . '<br/>';
    }
  }
}
?>

thats pretty much my code. i thought this might work, as with following line i would give new value to stock before exiting "if" function. but i guess im wrong

$item['stock'] = $stock_quantity;

any suggestions would be welcome

EDIT1: what im trying to do is compare id from $items array with id from $orders. if it matches from stock subtract quantity and display the remaining stock. hope its more clear

Answer 1

If you change foreach ($items as $item) to foreach ($items as &$item) it will change $item. Adding a & before a variable will make it a reference and not a new object. This way when you change item it will change the original item.

Answer 2

A foreach loop works by copying each value into a temporary variable.

If you want to edit the original array, you have two solutions :

Either pass the value with a reference, using & :

foreach ($items as &$item) {
    /*...*/
    $item['stock'] = $stock_quantity;
}

Or use the $key=>$value notation and edit the original array :

foreach ($items as $key => $item) {
    /*...*/
    $items[$key]['stock'] = $stock_quantity;
}

Answer 3

$items = array(
    array('id' => 34, 'name' => 'Kompiuterius ASUS ASX89', 'price' => 639.00, 'stock' => 3),
    array('id' => 1008, 'name' => 'Monitorius AOC 27IPS', 'price' => 223.00, 'stock' => 7),
    array('id' => 965, 'name' => 'Tracer kilimėlis pelytei', 'price' => 2.00, 'stock' => 20),
    array('id' => 567, 'name' => 'Pelytė Logitech A52', 'price' => 16.00, 'stock' => 14),
    array('id' => 1123, 'name' => 'Klaviatūra Razer Chroma 2016', 'price' => 109.00, 'stock' => 6)
);
$orders = array(
    array('purchase_date' => '2016-11-12', 'item_id' => 34, 'quantity' => 1),
    array('purchase_date' => '2016-11-12', 'item_id' => 1008, 'quantity' => 2),
    array('purchase_date' => '2016-11-13', 'item_id' => 965, 'quantity' => 1),
    array('purchase_date' => '2016-11-15', 'item_id' => 1123, 'quantity' => 4),
    array('purchase_date' => '2016-11-11', 'item_id' => 34, 'quantity' => 2)
);

foreach ($orders as $order){
    $purchase_id = $order['item_id'];
    $purchase_quantity = $order['quantity'];

    foreach ($items as &$item){
        $stock_id = $item['id'];
        $stock_quantity = $item['stock'];

        if ($purchase_id == $stock_id) {
            $stock_quantity = $stock_quantity - $purchase_quantity;
            $item['stock'] = $stock_quantity;
            echo 'Prekiu, pazymetu numeriu ' . $stock_id . ' liko: ' . $stock_quantity . ' vnt. ' . '<br/>';
        }
        unset($item);
    }
}

Make sure you add reference & before the foreach 's temporary variable if you need to manipulate the current element.

Once you're done with the foreach loop, remove the reference of the temporary variable using unset() function.

Therefore the variable will be destroyed otherwise it will still be accessible outside of foreach since it's still a reference variable.

For more information about this, you could refer to the following post:

Strange behavior Of foreach