Quick question - merging two or more arrays without reindexing

[eluser]xwero[/eluser]
You are right, i guess there is no function to merge arrays preserving the keys.

from the comments on php.net

Code:

<?php

$a=array('a'=>'a1','b.'=>'a2','a3','a4','a5');
$b=array(100=>'b1','b2','a'=>'b3','b4');

$a+=$b;

print_r($a);

?>

output:

[a] => a1
[b.] => a2
[0] => a3
[1] => a4
[2] => a5
[100] => b1
[101] => b2
[102] => b4

using the += operator doesn't causes errors when two keys are the same but the value for the first key is saved instead of overwritten by the second value of the same key.

[eluser]TheFuzzy0ne[/eluser]
I think everyone seems to have a different perception of what it is I'm actually trying to achieve, so I will tell you exactly what I my goal is. In my forum, I require a select box which shows the forum structure, but uses indentation so you can see the structure clearly. So it would look something like this (using CodeIgniter's forum as an example forum structure):

Code:

Forum Home
    The CodeIgniter Lounge
        Introduce Yourself!
        The Lounge
    CodeIgniter Development Forums
        CodeIgniter Discussion
        Code and Application Development
        Ignited Code
        Job Board
        Feature Requests
        Bug Reports
        Wiki Article Discussions

I need this in an array so I can use it with form_dropdown, so that might look something like this:

Code:

Array
(
    [1] => Forum Home
    [54] =>     The CodeIgniter Lounge
    [59] =>         Introduce Yourself!
    [55] =>         The Lounge
    [48] =>     CodeIgniter Development Forums
    [49] =>         CodeIgniter Discussion
    [53] =>         Code and Application Development
    [58] =>         Ignited Code
    [65] =>         Job Board
    [52] =>         Feature Requests
    [51] =>         Bug Reports
    [71] =>         Wiki Article Discussions
)

The array key is the ID of the forum, and will be used as the value for the select option.

As I use MPTT for my forum structure, I need to convert the tree itself into an array, which requires a bit of recursion. Here's the tree:

Code:

Array
(
    [id] => 1
    [title] => Forum Home
    [children] => Array
        (
            [0] => Array
                (
                    [id] => 54
                    [title] => The CodeIgniter Lounge
                    [children] => Array
                        (
                            [0] => Array
                                (
                                    [id] => 59
                                    [title] => Introduce Yourself!
                                )
                            [1] => Array
                                (
                                    [id] => 55
                                    [title] => The Lounge
                                )
                        )
                )
            [1] => Array
                (
                    [id] => 48
                    [title] => CodeIgniter Development Forums
                    [children] => Array
                        (
                            [0] => Array
                                (
                                    [id] => 49
                                    [title] => CodeIgniter Discussion
                                )
                            [1] => Array
                                (
                                    [id] => 53
                                    [title] => Code and Application Development
                                )
                            [2] => Array
                                (
                                    [id] => 58
                                    [title] => Ignited Code
                                )
                            [3] => Array
                                (
                                    [id] => 65
                                    [title] => Job Board
                                )
                            [4] => Array
                                (
                                    [id] => 52
                                    [title] => Feature Requests
                                )
                            [5] => Array
                                (
                                    [id] => 51
                                    [title] => Bug Reports
                                )
                            [6] => Array
                                (
                                    [id] => 71
                                    [title] => Wiki Article Discussions
                                )
                        )
                )
        )
)

Here's the function:

Code:

function forum_dropdown_options($tree, $indent_level=0)
{
    $ret = array();
    if (isset($tree['id']) && isset($tree['title']))
    {
        $ret[$tree['id']] = str_repeat('    ', $indent_level).$tree['title'];
        
        if (isset($tree['children']))
        {
            foreach ($tree['children'] as $forum)
            {
                $ret += forum_dropdown_options($forum, $indent_level +1);
            }
        }
    }
    
    return $ret;
}

And here's the resulting array:

Code:

Array
(
    [1] => Forum Home
    [54] =>     The CodeIgniter Lounge
    [59] =>         Introduce Yourself!
    [55] =>         The Lounge
    [48] =>     CodeIgniter Development Forums
    [49] =>         CodeIgniter Discussion
    [53] =>         Code and Application Development
    [58] =>         Ignited Code
    [65] =>         Job Board
    [52] =>         Feature Requests
    [51] =>         Bug Reports
    [71] =>         Wiki Article Discussions
)

Thanks, everyone.