How to process groups of duplicate fields and organize by common field key - PHP / Array

Looking to mimic what's going on on this website where you can add multiple field groups: When you click "add another card", it duplicates the field -- I've got this covered with jquery and clone(). However, if you input two gift cards with the same amount, on the next step they've combined the quantities for those gift cards into one group. So here's a scenario that I'm facing and the output that I would like to see:

User Input:

Field Group 1 -- Amount: $100 Quantity: 1
Field Group 2 -- Amount: $75 Quantity: 2
Field Group 3 -- Amount: $100 Quantity: 1

Desired Output on Next Page:

$100 Gift Card Group: 2
$开发者_JAVA技巧75 Gift Card Group: 2

I've been searching for different ways to do this and can't find anything, please help!!

For the inputs, I would use names like denomination[], quantity[], since we are processing arrays. On the next page, do a print_r() on $_POST, and then you can do a foreach() loop to combine quantities of the same denomination.

Now, suppose $foo is our (cleaned up) $_POST. Please perform a pre-processing loop to clean up the inputs; e.g. discarding invalid denominations/quantities as required.

Once this is done, we end up with $foo like:

<?php
// cleaned up $_POST
$foo = array(
    'denomination' => array(100, 75, 100),
    'quantity' => array(1, 2, 1),
);

$bar = array();
foreach ($foo['denomination'] as $d => $denomination) {
    if (array_key_exists($denomination, $bar)) { // denomination exists
       $bar[$denomination] += $foo['quantity'][$d];
    } else { // new denomination
       $bar[$denomination] = $foo['quantity'][$d];
    }
}
print_r($bar); die; // debug
?>

The output is:

Array(
    [100] => 2,
    [75] => 2
)