Question

I use PHP and mySQL with Idiorm. That might not be relevant.

My PHP array

• It’s a relationship between parents and childs.
• 0 is the root parent.
• Example: Root parent 0 have the child 33 which have the child 27 which have
  the child 71.

This array structure can be changed if needed for solving the problem.

array (
  33 => 
    array (
      0 => '27',
      1 => '41',
  ),
  27 => 
    array (
      0 => '64',
      1 => '71',
  ),
  0 => 
    array (
      0 => '28',
      1 => '29',
      2 => '33',
  ),
)

My hierarchical result

Something like this, but as an array…

  0 => 
      28
      29
      33
         27 =>
               64
               71
         41

Information

• The depth are unkown and it can be unlimited. I tried foreach, but it might not be the way.

My own thoughts

• Some recursive function?
• Some while loops?

I tried both of the above, just got a mess. It’s a brainer.

Answer 1

The suggestion by @deceze worked. However the input array needs to change a litte, like this…

$rows = array(
    array(
        'id' => 33,
        'parent_id' => 0,
    ),
    array(
        'id' => 34,
        'parent_id' => 0,
    ),
    array(
        'id' => 27,
        'parent_id' => 33,
    ),
    array(
        'id' => 17,
        'parent_id' => 27,
    ),
);

From https://stackoverflow.com/a/8587437/476:

function buildTree(array $elements, $parentId = 0) {
    $branch = array();

    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = buildTree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[] = $element;
        }
    }

    return $branch;
}

$tree = buildTree($rows);

print_r( $tree );