PHP Multi-Dimensional Array w/Parent ID to Category Taxonomy Array, Ebay Style

Question

Going for days now, ready to quit. I make a call to eBay's trading API to return a list of categories. The array below shows how these categories are returned from the API. I am trying like hell to arrange it into a taxonomy like the first gray box below.

Do note that the number at the beginning of each line is the id of the final category for that particular line.

3270: Vehicle Electronics & GPS
175716: Vehicle Electronics & GPS > Car Audio
18805: Vehicle Electronics & GPS > Car Audio > Car Subwoofers
18795: Vehicle Electronics & GPS > Car Audio > Car Amplifiers
39754: Vehicle Electronics & GPS > Car Audio > Car Audio In-Dash Units

I have greatly shortened this array to one example. Many categories will be pumped through to build the taxonomy.

The CategoryLevel can start at any number and it can end at any number. In this example, it starts at 2 and the highest level is 4.

Array
(
    [3270] => Array
        (
            [CategoryID] => 3270
            [CategoryLevel] => 2
            [CategoryName] => Vehicle Electronics & GPS
            [CategoryParentID] => 293
        )

    [175716] => Array
        (
            [CategoryID] => 175716
            [CategoryLevel] => 3
            [CategoryName] => Car Audio
            [CategoryParentID] => 3270
        )


    [79839] => Array
        (
            [CategoryID] => 79839
            [CategoryLevel] => 4
            [CategoryName] => Signal Processors
            [CategoryParentID] => 175716
            [LeafCategory] => true
        )

    [18805] => Array
        (
            [CategoryID] => 18805
            [CategoryLevel] => 4
            [CategoryName] => Car Subwoofers
            [CategoryParentID] => 175716
            [LeafCategory] => true
        )

    [18795] => Array
        (
            [CategoryID] => 18795
            [CategoryLevel] => 4
            [CategoryName] => Car Amplifiers
            [CategoryParentID] => 175716
            [LeafCategory] => true
        )

    [39754] => Array
        (
            [CategoryID] => 39754
            [CategoryLevel] => 4
            [CategoryName] => Car Audio In-Dash Units
            [CategoryParentID] => 175716
            [LeafCategory] => true
        )


)

Thank you in advance for your help!

Answer 1

Edit: Again, fixed error.

<?php
require_once("samplearray.php");

function makeNestedData($data){
    //create a nested tree using the above structure
    $nested = array();

    //loop over each category
    foreach($data as &$category){
        //is there is no children array, add it
        if(!isset($category['Children'])){
            $category['Children'] = array();
        }
        //check if there is a matching parent
        if(isset($data[$category['CategoryParentID']])){
            //add this under the parent as a child by reference
            if(!isset($data[$category['CategoryParentID']]['Children'])){
                $data[$category['CategoryParentID']]['Children'] = array();
            }
            $data[$category['CategoryParentID']]['Children'][$category['CategoryID']] = &$category;
        //else, no parent found, add at top level
        } else {
            $nested[$category['CategoryID']] = &$category;
        }
    }
    unset($category);
    return $nested;
}

//now flatten out the nested array recursively
function flattenNested($nested, $parent=''){
    $out = array();
    foreach($nested as $category){
        $categoryName = $parent.$category['CategoryName'];
        $out[$category['CategoryID']] = $categoryName;
        //recurse for each child
        $out += flattenNested($category['Children'], $categoryName.' > ');
    }
    return $out;
}

$result = flattenNested(makeNestedData($array));
print_r($result);

Outputs:

Array
(
    [3270] => Vehicle Electronics & GPS
    [175716] => Vehicle Electronics & GPS > Car Audio
    [79839] => Vehicle Electronics & GPS > Car Audio > Signal Processors
    [18805] => Vehicle Electronics & GPS > Car Audio > Car Subwoofers
    [18795] => Vehicle Electronics & GPS > Car Audio > Car Amplifiers
    [39754] => Vehicle Electronics & GPS > Car Audio > Car Audio In-Dash Units
)

Output is an array with the right side category id as the key and the value is a string with category text.

This may seem like a complicated or unnecessary way to do this, but this is really one of the better ways IMO because it will handle any order for the categories and any number of nested levels. The only limit would have to do with the recursion and possibly memory but I tried to use references where possible to keep that memory footprint as small as possible.

Example: http://codepad.viper-7.com/Fke5OA