The Cart in Codeigniter 3

New at the cart and struggling a little.

I am trying to send multiple updates through a multidimensional array from the view to the controller and I am having troubles, below is my view code:

Code:

<?php $i = 1; ?>
               <?php foreach ($this->cart->contents() as $items): ?>                
               <tr class="item first">
                   
                   <?php echo form_hidden($i.'[rowid]', $items['rowid']); ?>
                   
                   <td class="thumb"><a href=""><img src="img/catalog/shopping-cart-thumb.jpg" alt="<?php echo $items['name']; ?>"/></a></td>
                   <td class="name"><a href=""><?php echo $items['name']; ?></a></td>
                   <td class="price"><?php echo $this->cart->format_number($items['price']); ?></td>
                   <td class="qnt-count">
                       <a class="incr-btn" href="#">-</a>
                       <?php echo form_input(array('name' => $i.'[qty]', 'value' => $items['qty'], 'maxlength' => '2', 'size' => '2')); ?>
                       <a class="incr-btn" href="#">+</a>
                   </td>
                   <?php $total = $this->cart->format_number($items['price'])*$items['qty']; ?>
                   <td class="total">QR <?php echo $total ?></td>
               </tr>
               <?php $i++; ?>
               <?php endforeach; ?>  

I have pretty much copied the code from the user guide but I am a little unsure on how to update the cart in the controller, I have started the below:

PHP Code:

function update_cart() {
        
        $data = array (
                'rowid' => ,
                'qty'   => ,
            );
        
$this->cart->update($data);
redirect('/shop/cart', 'refresh');
} 


I am a little unsure on how to create a multidimensional array and update all basket items.  I have it updating the last one but cant do them all.

Thanks for your help.