How to push two elements into a new row of a 2d array?

Question

I am working on a function that adds an item to a cart. If the item already exists in the cart, increase its quantity amount by 1. If it doesn't, I want to add the item array in the next position in the cart array. Here's my code that I am using where $add_to_cart is the item ID:

if ($add_to_cart) {
    $added = false;
    foreach ($cart as &$item){
        if ($item['id'] == $add_to_cart){
            $item['qty'] += 1;
            $added = true;
        }
    }
    if (!$added) {
        $cart[count($cart)]['id'] = $add_to_cart;
        $cart[count($cart)]['qty'] = 1;
    }
    $_SESSION[$session_id]['cart'] = $cart;
}

When I use this code, it appends the ID of the item as the second last element, then the qty value as the last element. How can I make this work?

Answer 1

Your problem is when you are adding new elements to the cart:

if (!$added){
    $cart[count($cart)]['id'] = $add_to_cart;
    $cart[count($cart)]['qty'] = 1;
}

You are calling count($cart) in each line. After the 1st line is called, the count is different, so the 2nd line adds a different element. What you want is to push an array onto the array. Try this:

if (!$added){
    $cart[] = array(
        'id' => $add_to_cart,
        'qty' => 1
    );
}

Answer 2

Restructure your shopping cart array to something like this:

array(
    'id' => 'qty',
    .
    .
    .
);

What I mean by that is that you don't have to loop through the array the way you do.

You can just check to see if the index at key is set, then increment the value at that index.

if (isset($item[$add_to_cart])) { // formerly if(array_key_exists($add_to_cart, $item)) {
    $item[$add_to_cart]++;
} else {
    $item[$add_to_cart] = 1;
}

By doing this your performance will go from O(n) to O(1) and you go from 11 lines of code to 5.

Answer 3

As @Matt said, you might restructure your shopping cart array. But if you really want to use your current cart structure :

$cart = array();

function add_item($cart, $item_id)
{
    if(is_array($cart))
    {
        $added = false;

        for($i=0; $i<count($cart); $i++)
        {
            if($cart[$i]['id'] == $item_id)
            {
                $cart[$i]['qty'] ++;
                $added = true;
                break;
            }
        }

        if($added == false)
        {
            $i = count($cart);

            $cart[$i]['id'] = $item_id;
            $cart[$i]['qty'] = 1;
        }
    }

    return $cart;
}

$cart = add_item($cart, 50);
$cart = add_item($cart, 50);
$cart = add_item($cart, 50);

$cart = add_item($cart, 25);
$cart = add_item($cart, 25);

$cart = add_item($cart, 10);

var_dump($cart);

It prints :

array
  0 => 
    array
      'id' => int 50
      'qty' => int 3
  1 => 
    array
      'id' => int 25
      'qty' => int 2
  2 => 
    array
      'id' => int 10
      'qty' => int 1

EDIT : WITH A BETTER STRUCTURE

$cart = array();

function add_item($cart, $item_id)
{
    if(is_array($cart))
    {
        if(array_key_exists($item_id, $cart))
        {
            $cart[$item_id]++;
        }
        else
        {
            $cart[$item_id] = 1;
        }
    }

    return $cart;
}

$cart = add_item($cart, 50);
$cart = add_item($cart, 50);
$cart = add_item($cart, 50);

$cart = add_item($cart, 25);
$cart = add_item($cart, 25);

$cart = add_item($cart, 10);

var_dump($cart);

It prints :

array
  50 => int 3
  25 => int 2
  10 => int 1