Sort objects hierarchically in recursive multidimensional arrays

recursive_sort_generic.php

<?php
$entries = yourGetEntriesFromDbFunction();  //The array with our retrieved DB entries
$entryRecords = array();                    //Our hierarchy will be created in this array
//We will track the path of each entry here, with an array
//for each entry containing the ids of all its ancestors:
$entryPaths = array();
foreach ($entries as $entry) {
    //Create a new key inside each entry to store its children:
    $entry['children'] = array();
    $entryPaths[$entry['id']] = array();    //Make a space for the path of the entry
    if ($entry['parent'] === NULL) {        //If top level, just insert into the hierarchy array
        $entryRecords[$entry['id']] = $entry;
    } else {
    	$pathRef =& $entryRecords;          //Save a reference to the top level of our hierarchy
        //Traverse our current hierarchy based on the path of the entry's parent by reassigning a
        //single variable by reference to the children container of each level in the hierarchy:
        foreach ($entryPaths[$entry['parent']] as $path) {
    		$pathRef =& $pathRef[$path]['children'];
    	}
        //Once we reach the entry's parent's children container, just add the entry to it:
        $pathRef[] = $entry;
        //Register the entry's path by first copying parent's path
        $entryPaths[$entry['id']] = $entryPaths[$entry['parent']];
    }
    $entryPaths[$entry['id']][] = $entry['id']; //Finally add the id of the entry to its path
}