Sort MPTT resultset into a multidimensional array PHP

Question

I have been experimenting with the Modified Pre-Order Tree Traversal Pattern, my test case code is returning the results as expected however I am having trouble converting the 2D array into a multi-dimensional array to present it.

Here is an example of a 3 level menu result, I need to convert this into a multi-dimensional array so that I can iterate it in TAL:

Array
(
    [0] => Array
        (
            [CategoryID] => 1
            [ParentID] => 0
            [CategoryName] => Default Parent
            [lt] => 1
            [rt] => 14
            [tree_depth] => 1
        )

    [1] => Array
        (
            [CategoryID] => 8
            [ParentID] => 1
            [CategoryName] => SysAdmin
            [lt] => 2
            [rt] => 7
            [tree_depth] => 2
        )

    [2] => Array
        (
            [CategoryID] => 2
            [ParentID] => 8
            [CategoryName] => Linux
            [lt] => 3
            [rt] => 4
            [tree_depth] => 3
        )

    [3] => Array
        (
            [CategoryID] => 3
            [ParentID] => 8
            [CategoryName] => Windows
            [lt] => 5
            [rt] => 6
            [tree_depth] => 3
        )

    [4] => Array
        (
            [CategoryID] => 5
            [ParentID] => 1
            [CategoryName] => Code
            [lt] => 8
            [rt] => 13
            [tree_depth] => 2
        )

    [5] => Array
        (
            [CategoryID] => 6
            [ParentID] => 5
            [CategoryName] => PHP
            [lt] => 9
            [rt] => 10
            [tree_depth] => 3
        )

    [6] => Array
        (
            [CategoryID] => 7
            [ParentID] => 5
            [CategoryName] => Perl
            [lt] => 11
            [rt] => 12
            [tree_depth] => 3
        )

)

I need to structure the data so that every parent has a 'Children' key which is an array of arrays repeated, with no limitation on the amount of children a parent/child/grandchild can have, the tree_depth key is worked out automatically by the DBMS, so I simply need to alter the structure of the array.

Any pointers greatly appreciated, I have played with usort() and array_walk_recursive to no avail.

Thanks in advance

Answer 1

I think a simple foreach can do the trick here (with the help of references):

Set up a $menu associative array $cat_id => $element_details_anb_children:

$menu = array(); $ref = array();
foreach( $tree as $d ) {
    $d['children'] = array();
    if( isset( $ref[ $d['ParentID'] ] ) ) { // we have a reference on its parent
        $ref[ $d['ParentID'] ]['children'][ $d['CategoryID'] ] = $d;
        $ref[ $d['CategoryID'] ] =& $ref[ $d['ParentID'] ]['children'][ $d['CategoryID'] ];
    } else { // we don't have a reference on its parent => put it a root level
        $menu[ $d['CategoryID'] ] = $d;
        $ref[ $d['CategoryID'] ] =& $menu[ $d['CategoryID'] ];
    }
}

This should build two arrays: the multidimensional array you want ($menu) and a flat array which only holds references for each category. On each iteration it nests the category into its parent if it already exists (which is why I keep the reference table). Of course it works only if your initial $tree array is ordered (i.e. the parent comes before its children).