Q:

Combining multiple associative arrays efficiently on an ID key

I have a bunch of php arrays that look like this (please don't ask why, I'm just doing my job...All I will say is EAV...):
$firstNames = ([accountId] => 100, [firstName] => 'John'
               [accountId] => 101, [firstName] => 'Fred');

$lastNames =  ([accountId] => 100, [lastName] => 'Doe'
               [accountId] => 101, [lastName] => 'Bloggs');

$city      =  ([accountId] => 100, [city] => 'New York'
               [accountId] => 101, [city] => 'Cambridge');

$country   =  ([accountId] => 100, [country] => 'USA'
               [accountId] => 101, [country] => 'UK');

etc etc.
I have to combine them into one array:
$userDetails =  ([accountId] => 100, [firstName] => "John", [lastName] => "Doe", 
                 [city] => "New York", [country] => "USA");

My feeling is the correct answer would be to break these attributes out of EAV and model them correctly.  But I can't.  It would also be possible to do self-join upon self-join in the db, but I have simplified the example and this is not really possible - and I've been told to do it this way...There could be a bunch of additional fields tacked on as well, later.
So what is the best way to produce one associative array, merging on accountId in PHP?  Is there a function, or do I need to loop round and round etc.

A:

This nested foreach should do it:
$result = array();

foreach (array('firstNames' => 'firstName', 'lastNames' => 'lastName', 'city' => 'city', 'country' => 'country') as $srcArr => $arrKey) {
  foreach ($$srcArr as $item) {
    if (!isset($result[$item['accountId']])) {
      $result[$item['accountId']] = $item;
    } else {
      $result[$item['accountId']][$arrKey] = $item[$arrKey];
    }
  }
}

var_dump($result);

See it working

