How to efficiently combine two (or more) associative arrays with common keys

More generally, let's say we have two lists of different lengths with one common attribute:

list1: {
         {"orderID":1234, "FirstName":"shaheeb", "LastName":"roshan"},
         {"orderID":9183, "FirstName":"robert", "LastName":"gibbons"},
         {"orderID":2321, "FirstName":"chester"},
       }
list2: {
         {"orderID":1234, "cell":"555-555-5555", "email":"roshan@fake.com"},
         {"orderID":2321, "email":"chester@fake.com"},
       }

I would like these combined into:

list3: {
         {"orderID":1234, "FirstName":"shaheeb", "LastName":"roshan", "cell":"555-555-5555", "email":"roshan@fake.com"},
         {"orderID":9183, "FirstName":开发者_如何学C"robert", "LastName":"gibbons"},
         {"orderID":2321, "FirstName":"chester", "email":"chester@fake.com"},
       }

I'm primarily a PHP developer, and I came up with the following:

function mergeArrays($a1, $a2) {
    $larger = (count($a1) > count($a2)) ? $a1 : $a2;
    $smaller = ($larger == $a1) ? $a2 : $a1;
    $combinedArray = array();
    foreach ($larger AS $key=>$largerSet) {
        $combinedRow = array();
        if (isset ($smaller[$key]) ) {
            $combinedRow = $largerSet + $smaller[$key];
            $combinedArray[$key] = $combinedRow;
        }else {
            $combinedArray[$key] = $largerSet;
        }
    }
    return ($combinedArray);
}

If tested with the following:

$array1 = array("12345"=>array("OrderID"=>12345, "Apt"=>"blue"));
$array2 = array(
                "12345"=>array("OrderID"=>12345, "AnotherCol"=>"Goons", "furtherColumns"=>"More Data"),
                "13433"=>array("OrderID"=>32544, "Yellow"=>"Submarine")
            );

The mergeArrays($array1, $array2) outputs the following:

array(2) {
  [12345]=>
  array(4) {
    ["OrderID"]=>
    int(12345)
    ["AnotherCol"]=>
    string(5) "Goons"
    ["furtherColumns"]=>
    string(9) "More Data"
    ["Apt"]=>
    string(4) "blue"
  }
  [13433]=>
  array(2) {
    ["OrderID"]=>
    int(32544)
    ["Yellow"]=>
    string(9) "Submarine"
  }
}

But I just don't feel like this is the most elegant solution. For example, I should be able to combine n number of arrays. Not really sure how I would accomplish that. Also, just looking at that bit of code, I'm fairly certain there are far more effective ways to accomplish this requirement.

As a learning point, I am curious whether python experts would take this opportunity to show up us PHP folk :). For that matter, I am curious whether Excel/VBA can even handle this. That is where I started trying to solve this problem with the thought that "surely excel can handle lists!".

I am fully aware that there are many many variations of this question around SO. I have looked at several of these, and still felt that I should try my version out here.

Your thoughts are most appreciated.

Thank you!

SR

For a general solution in Python, for any number of lists:

orders = defaultdict(dict)
for order_list in order_lists:
    for order in order_list:
        orders[order['orderID']].update(order)

See it working online: ideone

A generic solution that can merge any number of dicts (or a list of dicts - if you have more than one list, just add them together before calling the function):

from collections import defaultdict

def merge_dicts_by_key(key, *dicts):
    return reduce(lambda acc,val: acc[val[key]].update(val) or acc,
                  dicts,
                  defaultdict(dict))

Call like so:

merge_dicts_by_key('orderId', dict1, dict2, dict3)

or, if you have lists of dicts:

merge_dicts_by_key('orderId', *list_of_dicts)
merge_dicts_by_key('orderId', *(list1 + list2))

Well, you could always replace your function with array_merge_recursive.