Re-arrange array elements if they meet a condition - php

Question

The array:
array(
'354' => array(
'parent' => 0
),
'370' => array(
'parent' => 0
),
'420' => array(
'parent' => 354
),
)
How can I move all elements that have the 'parent' value != 0, just after the element to which the key is the same as that parent value?
For example, the element with the 420 keys above needs to go after the element with the 354 key...

Answer 1

That's impossible in the general case. In your example it would work.
But here's another example:
Number | Parent
10 | 1
11 | 1
100 | 10
101 | 10
102 | 10
1000 | 100
1001 | 100
So you want that all the three rows 100, 101, 102 come directly after the row 10, which is impossible.
And between row 100 and 101 you probably want the rows 1000 and 1001, since their parent is 100.
[Update]
So there remain these questions:
Do you just need the nodes ordered so that each node is defined somewhere before it is used as a parent?
Do the direct children have to follow their parent directly, oder may there be some other nodes in between?
Is the parent ID always smaller than the node ID?

Answer 2

Maybe you're looking at a way to make a flat array have some sort of hierarchie?
This is a very simple case which will do that asuming your children always have a higher id than their parent.
<?php
$array = array(
'354' => array(
'parent' => 0
),
'370' => array(
'parent' => 0
),
'420' => array(
'parent' => 354
),
'550' => array(
'parent' => 420
),
);
/**
*
* This function will convert a flat array with elements to the proper hierarchy structure
* #param array $array
*/
function hierarchy(&$array) {
arsort($array);
foreach($array as $key => $value)
{
if($value['parent'])
{
$array[$value['parent']]['children'][$key] = $value;
unset($array[$key]);
}
}
asort($array);
return $array;
}
(print '<pre>' . print_r(hierarchy($array), true) . '</pre>');
Heres a testcase:
http://codepad.org/RT51uOfn