PHP Reorder array to reflect parent / id hierarchy - php

Question

How do I rearrange the following array
[0] => Array
(
[id] => 1
[parent_id] => 0
[name] => Accueil
)
[1] => Array
(
[id] => 2
[parent_id] => 0
[name] => Exposants
)
[2] => Array
(
[id] => 3
[parent_id] => 0
[name] => Visiteurs
)
[3] => Array
(
[id] => 4
[parent_id] => 0
[name] => Medias
)
[4] => Array
(
[id] => 5
[parent_id] => 0
[name] => Activités
)
[5] => Array
(
[id] => 6
[parent_id] => 1
[name] => Contact
)
[6] => Array
(
[id] => 7
[parent_id] => 3
[name] => Partenaires
)
[7] => Array
(
[id] => 8
[parent_id] => 2
[name] => News
)
So I come up with an array that reflects the hierarchy as shown by the id and parent_id fields? The array key is the ID field of array elements are parents. Inside this array is each time a child array that has its ID field as the key. Sample:
[1] => Array
(
[name] => Accueil
[children] => array(
[0] => bla,
[3] => bla2
)
)
[2] => Array
(
[name] => Something
[children] => array(
[4] => bla3,
)
)

Answer 1

Works for any depth and allows children to precede parents:
<?php
$p = array(0 => array());
foreach($nodes as $n)
{
$pid = $n['parent_id'];
$id = $n['id'];
if (!isset($p[$pid]))
$p[$pid] = array('child' => array());
if (isset($p[$id]))
$child = &$p[$id]['child'];
else
$child = array();
$p[$id] = $n;
$p[$id]['child'] = &$child;
unset($p[$id]['parent_id']);
unset($child);
$p[$pid]['child'][] = &$p[$id];
}
$nodes = $p['0']['child'];
unset($p);
?>
Use var_dump on the $nodes result to see the structure. It is close to what you suggested. The major difference is that the keys are not the ids.

Answer 2

You could make this more DRY, but it's a quick and dirty way to handle it. Also, you could remove 6 lines if you could guarantee that each child record has a valid parent record and that the valid parent record precedes the child record in the original array.
$sorted = array();
foreach( $orig_ary as $item ) {
if ( $item['parent_id'] === 0 ) {
if ( !array_key_exists( $item['id'], $sorted ) ) {
$sorted[ $item['id'] ] = array(
'name' => '',
'children' => array()
);
}
$sorted[ $item['id'] ]['name'] = $item['name'];
} else {
if ( !array_key_exists( $item['parent_id'], $sorted ) ) {
$sorted[ $item['parent_id'] ] = array(
'name' => '',
'children' => array()
);
}
$sorted[ $item['parent_id'] ]['children'][ $item['id'] ] = $item['name'];
}
}