Category hierarchy from array(cat id => parent id)

Question

i am trying to create a multidimensional array hierarchy from a simple array which contains pairs of category ids and parent ids. The categories can be a parent and a subcategor

Answer 1

I know, late to the party but it looks interesting...

/*
 * This is a 'multiway' tree where:
 *   a 'parent' can have any number of 'child' nodes
 *   therefore the 'parent node' must look like:
 *   [parentId] => array()
 *
 *   where [parentId] is the index of an array;
 */

It will insert one node at a time starting from the root node. It can get very expensive for large trees.

Working example at: Viper-7.com

The routine that does the work:

/**
 * Insert:  Find the 'parent' node
 *          if child not found then insert a 'node'
 *
 * @param array node passed by reference as the new node will be inserted
 * @param integer $parentId - root Id must be the lowest value
 * @param integer $childId
 * @return boolean  true if parentId found and processed
 */
function insertNode(&$node, $parentId, $childId) {

    if (isset($node[$parentId])) { // this node will be processed
        if (!isset($node[$parentId][$childId])) {
            $node[$parentId][$childId] = array(); // add child node
            return true;
        }
        return true; // end of processing
    }

    // check all the children of this node...
    foreach($node as &$child) { // need the reference
        if (insertNode($child, $parentId, $childId)) {
            return true;
        }
    }
    return false; // parentId not in the tree
}

Notes:

The node to be processed is passed by reference.
The processing will end when the 'parent' id is found 

The input node list as given is 'child' => 'parent' order which is unusual, it is ok, just remember that in the processing...

Process the input data:

$theTree = array(current($links) => array()); // root

// insert all the child nodes into the tree
foreach($links as $childId => $parentId) {
    $inserted = insertNode($theTree, $parentId, $childId);
}

// output the tree
echo '
', 'Children are in the same order as the input array.', '
';
    print_r($theTree);
echo '
';

The input list needs to be arraged so that the 'tree' will be loaded such that the parent of the child to be added must be in the tree already. i assume that the input list is in the required order already

Test data, sort and display:

# cat_id => parent_id
$links = array(
   1 => 0,
   2 => 1,
   3 => 2,

   4 => 0,
   5 => 4, // multiple children
  11 => 4,
  99 => 4,
  13 => 11,

   6 => 0
);

Output, i added a sub-tree to the original input...

Children are in the same order as the input array.
Array
(
    [0] => Array
        (
            [1] => Array
                (
                    [2] => Array
                        (
                            [3] => Array
                                (
                                )
                        )
                )
            [4] => Array
                (
                    [5] => Array
                        (
                        )

                    [11] => Array
                        (
                            [13] => Array
                                (
                                )
                        )
                    [99] => Array
                        (
                        )
                )
            [6] => Array
                (
                )
        )
  )