I am cracking my brain and can't find a good solution for my problem. I am trying to design a system that I can use for batch picking in our order system.

The point is that from a set of orders I want to pick 6 orders that are most equal to each other. In our warehouse most orders are them so we can safe a lot of time by picking some orders at the same time.

Assume I have the following array:

<?php

$data = [
    156 => [
        1,
        2,
        7,
        9,
    ],
    332 => [
        3,
        10,
        6
    ],
    456 => [
        1,
    ],
    765 => [
        7,
        2,
        10,
    ],
    234 => [
        1,
        9,
        3,
        6,
    ],
    191 => [
        7,
    ],
    189 => [
        7,
        6,
        3,
    ],
    430 => [
        10,
        9,
        1,
    ],
    482 => [
        1,
        2,
        7,
    ],
    765 => [
        1,
        5,
        9,
    ]
];
?>

The array key is the order id, and the values are the product ID's it contains. If I want to pick the top 3 orders which look at much like each other, where do I start?

Any help would be much appreciated!

Here is what i would do if I had the problem :

$topOrders = [];
foreach($data as $value):
    foreach($value as $order):
        if(isset($$order)):
            $$order++;
        else:
            $$order = 1;
        endif;
        $topOrders[$order] = $$order;
    endforeach;
endforeach;

print_r($topOrders);

In $topOrders, you have an array that contains as key the ID, and as value you got the number of orders. All you have to do is to sort your array to get your top 3.

1. Step

Sort productId inside order (ASC)

2. Step

In loop check difference (array_diff) in each order to each other.
Create array with defference. For example:

$diff = [
    '156' => [ //order id
        '234' => 4, // with order 234 has 4 differences
        '332' => 7, // with order 332 has 7 differences
        // and so on...
    ],
]

3. Step

Order $diff by ASC and receive order with less differences.

Improvement

Also you could add total size of products in order for compare with difference. For example, If you have an order with 100 products and 10 diffs - it's better than order with 10 products and 9 diffs.