Create Dynamic Array Key Structure in PHP - php

Question

I have documents stored on my server, and their information like title, filepath, date, category, etc., stored in a database. My goal is to be able to group the documents together by their categories. The document's category is stored in the database as a string like "COVID-19 | Guidance | Mortuary Affairs", and I want to convert it to an array like the following:
[
"COVID-19" => [
"Guidance"=> [
"Mortuary Affairs" => [
// Where the document info will be
]
]
]
]
The first step would be looping through the documents and exploding each category by the | delimiter:
foreach($all_documents as $document)
{
$categories = array_map('trim', explode('|', $document['category']));
}
Doing so results in the following:
[
"COVID-19",
"Guidance",
"Mortuary Affairs"
]
How would I then take this array and turn it into the nested array displayed at the top?

Answer 1

After the creation of the array with categories, you could iterate those categories and "drill" down a result object with a node-reference -- creating any missing properties, and then referencing them. Finally append the document to the deepest node's array (so multiple documents can end up at the same place):
$result = [];
foreach ($all_documents as $document) {
$categories = array_map('trim', explode('|', $document['category']));
$node =& $result; // reference the "root"
$last = array_pop($categories);
foreach ($categories as $category) {
if (!isset($node[$category])) $node[$category] = []; // create child
$node =& $node[$category]; // change the reference to the child
}
$node[$last][] = $document; // append document to this list
}
At the end $result will have the desired hierarchical structure.