PHP parent/child iteration in single-dimension array [duplicate] - php

Question

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create array tree from array list [duplicate]
(9 answers)
Closed 5 years ago.
I am at a little bit of a loss as to how to approach this, I suspect foreach is not the right answer, and I am aware of the existence of array_walk() and RecursiveArrayIterator, but I have no real-world experience of using either, so I could do with a bit of a pointer in the right direction. (I am working with PHP 7.1.9 if it makes any difference to the answer).
Source data
I have a single-dimension array that contains a parent/child tree of objects. You can assume the tree has unknown and variable nesting depth. A basic example would look like the following :
$sampleParent=array("id"=>101,"level"=>1,"parent_id"=>1,"name"=>"parent","otherparam"=>"bar");
$sampleChildD1=array("id"=>234,"level"=>2,"parent_id"=>101,"name"=>"level1","otherparam"=>"bar");
$sampleChildD2=array("id"=>499,"level"=>3,"parent_id"=>234,"name"=>"level2","otherparam"=>"bar");
$sampleTree=array($sampleParent,$sampleChildD1,$sampleChildD2);
Desired output
The ultimate goal is to output HTML lists (i.e. <ul><li></li></ul>), one list per parent. Nesting of children achieved by nesting <ul> tags. So for my example above :
<ul>
<li>
parent
</li>
<ul>
<li>
level1
<ul>
<li>
level2
</li>
</ul>
</li>
</ul>
</ul>

Answer 1

You can extend RecursiveArrayIterator:
class AdjacencyListIterator extends RecursiveArrayIterator
{
private $adjacencyList;
public function __construct(
array $adjacencyList,
array $array = null,
$flags = 0
) {
$this->adjacencyList = $adjacencyList;
$array = !is_null($array)
? $array
: array_filter($adjacencyList, function ($node) {
return is_null($node['parent_id']);
});
parent::__construct($array, $flags);
}
private $children;
public function hasChildren()
{
$children = array_filter($this->adjacencyList, function ($node) {
return $node['parent_id'] === $this->current()['id'];
});
if (!empty($children)) {
$this->children = $children;
return true;
}
return false;
}
public function getChildren()
{
return new static($this->adjacencyList, $this->children);
}
}
Then you can traverse this iterator with RecursiveIteratorIterator, or you can extend the former to somewhat semi-automatically decorate the tree with HTML:
class UlRecursiveIteratorIterator extends RecursiveIteratorIterator
{
public function beginIteration()
{
echo '<ul>', PHP_EOL;
}
public function endIteration()
{
echo '</ul>', PHP_EOL;
}
public function beginChildren()
{
echo str_repeat("\t", $this->getDepth()), '<ul>', PHP_EOL;
}
public function endChildren()
{
echo str_repeat("\t", $this->getDepth()), '</ul>', PHP_EOL;
echo str_repeat("\t", $this->getDepth()), '</li>', PHP_EOL;
}
}
Having this two classes you can iterate your tree like this:
$iterator = new UlRecursiveIteratorIterator(
new AdjacencyListIterator($sampleTree),
RecursiveIteratorIterator::SELF_FIRST
);
foreach ($iterator as $leaf) {
echo str_repeat("\t", $iterator->getDepth() + 1);
echo '<li>', '', $leaf['name'], '';
echo $iterator->hasChildren() ? '' : '</li>', PHP_EOL;
}
Here is working demo.
Take a notice, that str_repeat and PHP_EOL used here only for presentation purpose and should be removed in real life code.

Answer 2

May I suggest to do this in an OOP manner?
I'd create an object with the properties and a list of children. If you like, you could also add a link from a child to its parent, as in this sample
class TreeNode {
// string
public $name;
// integer
public $id;
// TreeNode
public $parent;
// TreeNode[]
public $children;
}
With this structure, it should be very straight forward to iterate it using foreach.