PHP array_merge not doing exactly what i need it to do - php

Question

Ok so here is my first array:
(
[1] => Array
(
[27] => Array
(
[product_id] => 27
[type] => hardware
[step_number] => 1
)
[372] => Array
(
[product_id] => 372
[type] => hardware
[step_number] => 1
)
[92] => Array
(
[product_id] => 92
[type] => hardware
[step_number] => 1
)
)
[2] => Array
(
[335] => Array
(
[product_id] => 335
[type] => hardware
[step_number] => 2
)
[62] => Array
(
[product_id] => 62
[type] => hardware
[step_number] => 2
)
[356] => Array
(
[product_id] => 356
[type] => hardware
[step_number] => 2
)
)
and here is my second array
(
[1] => Array
(
[655] => Array
(
[product_id] => 655
[type] => optional
[step_number] => 1
)
[54] => Array
(
[product_id] => 54
[type] => optional
[step_number] => 1
)
[554] => Array
(
[product_id] => 554
[type] => optional
[step_number] => 1
)
)
[2] => Array
(
[33] => Array
(
[product_id] => 33
[type] => optional
[step_number] => 2
)
[612] => Array
(
[product_id] => 612
[type] => optional
[step_number] => 2
)
[5] => Array
(
[product_id] => 5
[type] => optional
[step_number] => 2
)
)
[3] => Array
(
[444] => Array
(
[product_id] => 444
[type] => optional
[step_number] => 3
)
[6] => Array
(
[product_id] => 6
[type] => optional
[step_number] => 3
)
[53] => Array
(
[product_id] => 53
[type] => optional
[step_number] => 3
)
)
Basically what i need is the second array appended to the end of the first array with the keys of the first array preserved the keys and changing the step_number to the new key so the final keys looks like
(
[1] => Array
(
[27] => Array
(
[step_number] => 1)
....
[2] => Array
(
[335] => Array
(
[step_number] => 2)
....
[3] => Array
(
[655] => Array
(
[step_number] => 3)
....
[4] => Array
(
[33] => Array
(
[step_number] => 4)
....
[5] => Array
(
[444] => Array
(
[step_number] => 5)
....
but when i do
$all = array_merge($first, $second);
the keys are
(
[0] => Array
[1] => Array
[2] => Array
[3] => Array
[4] => Array
Is that possible to do....

Answer 1

Try array_merge_recursive .. http://php.net/array_merge_recursive

Answer 2

This is also from the manual on array_splice if you're just looking to append your 2nd array onto the first (http://php.net/manual/en/function.array-push.php):
array_splice($first, count($first), 0, $second);

Answer 3

Iterating over the first set of keys, then using the Union array operator should do the trick.
//$first = array(...);
//$second = array(...);
foreach ($second as $key => $value)
{
if (!isset($first[$key]))
{
$first[$key] = array();
}
$first[$key] += $value;
}