Question

I am looking for an example how a recursive array passed as parameter for RecursiveArrayIterator should be structured. I have a mysql table with id, parent_id and title:

id    parent_id   title
-----------------|-------------------
1         0      | Item 1
2         1      | Item 2
3         1      | Item 3
4         3      | Item 4
5         4      | Item 5

I would like to create an array from the table, that can be passed to RecursiveArrayIterator to build trees, menus, options and so on. I have tried this “build_tree” function https://stackoverflow.com/a/8587437/1746522 to create an array from mysql table. The resulted array looks like:

array (size=2)
  0 => 
    array (size=3)
      'id' => string '1' (length=1)
      'title' => string 'Item 1' (length=6)
      'parent_id' => string '0' (length=1)
      'children' => 
        array (size=2)
          0 => 
            array (size=3)
              ...
          1 => 
            array (size=3)
              ...

But when I pass the resulted array to RecursiveArrayIterator it looks strange. E.g. using this function:

$array = new RecursiveArrayIterator($tree);
$iterater = new RecursiveIteratorIterator($array);  
foreach ($iterater as $key => $value) {
    $d = $iterater->getDepth();            
    echo "depth=$d k=$key v=$value\n";
}

I have the strange and unusable output like:

depth=0 k=0 v=Array
depth=1 k=id v=1
depth=1 k=title v=Item 1
depth=1 k=parent_id v=0
depth=2 k=0 v=Array
depth=3 k=id v=2
depth=3 k=title v=Item 2
depth=3 k=parent_id v=1
depth=4 k=0 v=Array
....

The depth is wrong, and it iterates through single values and not elements. Probably is the array passed to RecursiveArrayIterator is “malformed” and should be structured other way?

I have expected to see something like this:

depth=0 k=1 v=Array
depth=1 k=2 v=Array
depth=1 k=3 v=Array

where Array contains all values to the node, like parent_id and title and k is the id from the mysql column id.

Answer 1

My final solution with unlimited depth, only one query, all information from the table and access to all functions of RecursiveIteratorIterator like children and depth. I use two arrays in my solution.

Flat array

select * from table

and create flat array as usual:

$info[1] = array('parent_id' => 0, 'title' => 'Item 1');
$info[2] = array('parent_id' => 1, 'title' => 'Item 2');
$info[3] = array('parent_id' => 1, 'title' => 'Item 3');
$info[4] = array('parent_id' => 3, 'title' => 'Item 4');
$info[5] = array('parent_id' => 4, 'title' => 'Item 5');

use id column as array index.

Nested Array

Create nested array from $info that contains ONLY ids of the items:

function tree_structure($info, $parent = 0) {    
    foreach ($info as $row) {
        if ($row['parent_id'] == $parent)
            $struc[$row['id']] = tree_structure($info, $row['id']);
    }    
    return $struc;        
}

This array can be passed to RecursiveArrayIterator.

You have two arrays now:

• $info – (flat) contains all information about your nodes
• $struc – (recursive) contains the structure of the nodes

RecursiveArrayIterator

Start to work with RecursiveArrayIterator

    $array = new RecursiveArrayIterator($struc);
    $iterator = new RecursiveIteratorIterator($array, TRUE);
    $iterator->rewind();

    while ($iterator->valid()) {
        // Get the id
        $iterator->key();
        // Get the depth
        $iterator->getDepth();
        // Check if it has children
        $iterator->hasChildren();
        // Get the number of children
        sizeof($iterator->callGetChildren());
        // Get all information for the node from the flat array
        $info[$iterator->key()];

        $iterator->next();
    }

The line $info[$iterator->key()] in the code does the actual trick. With this line you have all information about your node without messing the structure.