php - Convert flat array to the multi-dimensional

Question

I have an array with tree data (by parent id). I want to convert it to multidimensional array. What is the best way to achieve that? Is there any short function for that?

Source array:

$source = array(
    '0' => array(
            'Menu' => array(
                    'id' => 45
                    'name' => 'Home'
                    'parent_id' => 1
            )
    )
    '1' => array(
            'Menu' => array(
                    'id' => 47
                    'name' => 'Get started'
                    'parent_id' => 1
            )
    )
    '2' => array(
            'Menu' => array(
                    'id' => 72
                    'name' => 'Attributes'
                    'parent_id' => 71
            )
    )
    '3' => array(
            'Menu' => array(
                    'id' => 73
                    'name' => 'Headings'
                    'parent_id' => 71
            )
    )
    '4' => array(
            'Menu' => array(
                    'id' => 75
                    'name' => 'Links'
                    'parent_id' => 71
            )
    )
    '5' => array(
            'Menu' => array(
                    'id' => 59
                    'name' => 'Images'
                    'parent_id' => 75
            )
    )
    '6' => array(
            'Menu' => array(
                    'id' => 65
                    'name' => 'Lists'
                    'parent_id' => 75
            )
    )
);

Some parents are missing from the source array. I would like the items with missing parent to be root. Result array:

$result = array(
    '0' => array(
            'Menu' => array(
                    'id' => 45
                    'name' => 'Home'
                    'parent_id' => 1
            )
            'Children' => array()
    )
    '1' => array(
            'Menu' => array(
                    'id' => 47
                    'name' => 'Get started'
                    'parent_id' => 1
            )
            'Children' => array()
    )
    '2' => array(
            'Menu' => array(
                    'id' => 72
                    'name' => 'Attributes'
                    'parent_id' => 71
            )
            'Children' => array()
    )
    '3' => array(
            'Menu' => array(
                    'id' => 73
                    'name' => 'Headings'
                    'parent_id' => 71
            )
            'Children' => array()
    )
    '4' => array(
            'Menu' => array(
                    'id' => 75
                    'name' => 'Links'
                    'parent_id' => 71
            )
            'Children' => array(
                    '0' => array(
                        'Menu' => array(
                            'id' => 59
                            'name' => 'Images'
                            'parent_id' => 75
                        )
                        'Children' => array()
                    )
                    '1' => array(
                        'Menu' => array(
                            'id' => 65
                            'name' => 'Lists'
                            'parent_id' => 75
                        )
                        'Children' => array()
                   )
            )
     )
);

Update: removed square brackets.

Answer 1

I don't think there is a built-in function in PHP that does this.

I tried the following code, and it seems to work to prepare the nested array the way you describe:

$nodes = array();
$tree = array();
foreach ($source as &$node) {
  $node["Children"] = array();
  $id = $node["Menu"]["id"];
  $parent_id = $node["Menu"]["parent_id"];
  $nodes[$id] =& $node;
  if (array_key_exists($parent_id, $nodes)) {
    $nodes[$parent_id]["Children"][] =& $node;
  } else {
    $tree[] =& $node;
  }
}

var_dump($tree);

I wrote a similar algorithm in a PHP class I wrote for my presentation Hierarchical Models in SQL and PHP, but I was using objects instead of plain arrays.