Convert flat array to the multi-dimensional - php

Question

I have an array with tree data (by parent id). I want to convert it to multidimensional array. What is the best way to achieve that? Is there any short function for that?
Source array:
$source = array(
'0' => array(
'Menu' => array(
'id' => 45
'name' => 'Home'
'parent_id' => 1
)
)
'1' => array(
'Menu' => array(
'id' => 47
'name' => 'Get started'
'parent_id' => 1
)
)
'2' => array(
'Menu' => array(
'id' => 72
'name' => 'Attributes'
'parent_id' => 71
)
)
'3' => array(
'Menu' => array(
'id' => 73
'name' => 'Headings'
'parent_id' => 71
)
)
'4' => array(
'Menu' => array(
'id' => 75
'name' => 'Links'
'parent_id' => 71
)
)
'5' => array(
'Menu' => array(
'id' => 59
'name' => 'Images'
'parent_id' => 75
)
)
'6' => array(
'Menu' => array(
'id' => 65
'name' => 'Lists'
'parent_id' => 75
)
)
);
Some parents are missing from the source array. I would like the items with missing parent to be root. Result array:
$result = array(
'0' => array(
'Menu' => array(
'id' => 45
'name' => 'Home'
'parent_id' => 1
)
'Children' => array()
)
'1' => array(
'Menu' => array(
'id' => 47
'name' => 'Get started'
'parent_id' => 1
)
'Children' => array()
)
'2' => array(
'Menu' => array(
'id' => 72
'name' => 'Attributes'
'parent_id' => 71
)
'Children' => array()
)
'3' => array(
'Menu' => array(
'id' => 73
'name' => 'Headings'
'parent_id' => 71
)
'Children' => array()
)
'4' => array(
'Menu' => array(
'id' => 75
'name' => 'Links'
'parent_id' => 71
)
'Children' => array(
'0' => array(
'Menu' => array(
'id' => 59
'name' => 'Images'
'parent_id' => 75
)
'Children' => array()
)
'1' => array(
'Menu' => array(
'id' => 65
'name' => 'Lists'
'parent_id' => 75
)
'Children' => array()
)
)
)
);
Update: removed square brackets.

Answer 1

I don't think there is a built-in function in PHP that does this.
I tried the following code, and it seems to work to prepare the nested array the way you describe:
$nodes = array();
$tree = array();
foreach ($source as &$node) {
$node["Children"] = array();
$id = $node["Menu"]["id"];
$parent_id = $node["Menu"]["parent_id"];
$nodes[$id] =& $node;
if (array_key_exists($parent_id, $nodes)) {
$nodes[$parent_id]["Children"][] =& $node;
} else {
$tree[] =& $node;
}
}
var_dump($tree);
I wrote a similar algorithm in a PHP class I wrote for my presentation Hierarchical Models in SQL and PHP, but I was using objects instead of plain arrays.

Answer 2

I wrote this variant considering root parent_id is 0 or missing. No matter children after parents in DB ($source) or not.
$source_by_id = array();
foreach ($source as &$row){
$source_by_id[$row['id']] = &$row;
}
foreach ($source_by_id as $id => &$row){
$source_by_id[ intval($row['parent_id']) ]['children'][$id] = &$row;
}
// remove cycling itself
unset($source_by_id[0]['children'][0]);
$result = $source_by_id[0]['children'];
Result array keys are appropriate ids. Enjoy!

Answer 3

I was looking for an example of how to do this, with categories. This example assumes that parents will always have a parent id of '0'. The example is using ZF2.
No references, or recursion. The trick is in the output, you look for the [0] index, and for the children, you specify the parent_id as the index.
$categoryLookup = $this->getCategoryLookup($associateById=true);
if ($assignedCategories) {
$categoryHeirarchy = array();
foreach($assignedCategories as $assignedCategory) {
$child = $categoryLookup[$assignedCategory->category_id];
$parent = $categoryLookup[$child->parent_id];
$categoryHeirarchy[$child->parent_id][] = $categoryLookup[$child->category_id];
$categoryHeirarchy[$parent->parent_id][$parent->category_id] = $categoryLookup[$parent->category_id];
}
return $categoryHeirarchy;
}
<h3>Categories</h3>
<dl class="dl-horizontal">
<?php foreach($this->categoryHeirarchy[0] as $parent): ?>
<dt><?php echo $this->escapeHtml($parent->name); ?></dt>
<?php foreach($this->categoryHeirarchy[$parent->category_id] as $child): ?>
<dd><?php echo $this->escapeHtml($child->name); ?></dd>
<?php endforeach; ?>
<?php endforeach; ?>
</dl>