PHP While Loop Resolve - php

Question

I am having a bit of trouble resolving things in a PHP while loop. Basically I have an array in this form (easier to represent in JSON for brevity)
{
"node2": {
"rowid": "2",
"label": "Eco-Lights - Compact Fluorescent Lamps (CFL)",
"slug": "eco-lights-compact-fluorescent-lamps-cfl",
"prefix": "/categories",
"parent": "55",
"path": null,
"weight": "100",
"featured": "0",
"active": "0"
},
"node3": {
"rowid": "3",
"label": "Light Movers, Hangers and Accessories",
"slug": "light-movers-hangers-and-accessories",
"prefix": "/categories",
"parent": "59",
"path": null,
"weight": "100",
"featured": "0",
"active": "0"
}
}
This array is about 150 elements give or take a few. The key of the node is simply "node"+rowid for ease of lookup (in the next part)
What I am trying to do is take any node and go right up until its parent is zero (i/e has no parents) and on each iteration grab the label and slug of the parent element.
So far I have done this using a while loop as below. $this->categories is the array as above. The trouble is that the loop is incorrect and it's hitting 4gb of memory and doing around 5,000 loops for an array of 150 elements with roughly one parent each so it should be something less than 500 iterations.
public function ResolveCategoryUrl($id) {
$element=$element=$this->categories['node'.$id];
$parent=$element['parent'];
while(1) {
$prev=$element;
$element=$this->categories['node'.$element['parent']];
$parts[]=$element['slug'];
$breadcrumbs[]=['label'=>$element['label'],'url'=>$element['prefix'].$element['path'].$element['data']['url_postfix']];
$parent=$element['parent'];
if($parent<=1) {
break;
}
}
return [
'path'=>array_reverse($parts),
'breadcrumbs'=>$breadcrumbs
];
}
I cannot figure out how to tell PHP to take an element and work backward up to its parent until parent = 0 then return what I want from the function.
Sorry if the explanation is difficult, I have no other way to explain it!

Answer 1

This sounds like a basic reverse tree search (starting at a leaf node and working back up to the root). This is accomplished easily when using recursion. Something along these lines is probably what you're looking for:
function visitNode($nodeNum, $output = [])
{
$output[] = $nodeNum;
$element = $this->categories['node' . $nodeNum];
$parent = $element['parent'];
// Recursive case: keep searching until you're at the parent
if($parent != 0) {
return visitNode($parent, $output);
}
// Base Case
return $output;
}
The output of this function will be an array of your ids representing the chain of nodes visited on the search from your leaf node to its parent. The output of calling this on a parent node will be an array with a single entry.
You may need to put in another case to ensure that the category node + $nodeNum actually exists, but it may make more sense for that to be elsewhere.
Update
To use this function to solve your particular problem and build the breadcrumbs (getting the specific output you require):
$path = [];
$breadcrumbs = [];
$myStartNode = '3';
$pathIds = array_reverse(visitNode($myStartNode));
foreach($pathIds as $pathId) {
$element = $this->categories[$pathId];
$path[] = $element->slug;
$breadcrumbs[] = [
'label' => $element['label'],
'url' => $element['prefix'].$element['path'].$element['data']['url_postfix']
];
}
return [ 'path' => $path, 'breadcrumbs' => $breadcrumbs ];
The visitNode function above was mentioned solely to try to help solve the issue I believe that you're having difficulty with. Also, it's probably best to keep that logic outside what you're trying to do because you may be required to perform that same sort of tree traversal in another context that requires different output.

Answer 2

You said there is no [node0].
If you are certain that all nodes are in order (no missing numbers), then you can do something like:
$i = count($arrayData) //will give you number of nodes
And you can loop through your array with something like:
for ($a=$i, $a>=1; $a--)
{
$b = $arrayData[$a];
$label = $b['label'];
}