Question

I want a table of comments like so

id | comment | parent_id
--------------------------
1    text1        0
2    text2        1
3    text3        2
4    text4        3
5    text5        3
6    text6        5

I want to construct an array displaying the hierarchy of the parents and children. The tree should go back a undetermined number of generations. I don’t want to use nesting foreach loops as I’m not sure how deep it goes. That is why I’m here, I’m not sure of the best practice for a problem like this. I also want to display the depth in the array. Below is an example. It doesn’t really relate to table above, but hopefully gives you an idea of what I need.

array(
    "depth"=> 4
    "parent" => array(
        "id"=> 1,
        "comment" => "sometext1"
        "child_count" => 2,
        "children" => array(
            0 => array(
                "id" => 2
                "comment" => "sometext2",
                "child_count" => 0,
                "children" => null
            ),
            1 => array(
                "id" => 3
                "comment" => "sometext3"
                "child_count" => 1,
                "children" => array(
                    0 => array(
                        "id" => 2
                        "comment" => "sometext2",
                        "child_count" => 2,
                        "children" => array(
                            0 => array(
                                "id" => 2
                                "comment" => "sometext2",
                                "child_count" => 0,
                                "children" => null
                            ),
                            1 => array(
                                "id" => 2
                                "comment" => "sometext2",
                                "child_count" => 1,
                                "children" => array(
                                    "id" => 2
                                    "comment" => "sometext2",
                                    "child_count" => 0,
                                    "children" => null
                                )
                            )
                    )
                )
            )
        )
    )
)

I was going to use foreach and do a SQL statement to retrive that parent/childs children. ie

$sql = "SELECT * FROM comments WHERE parent = $parent_id";

Im not really looking for the code for all this, just a pseudo code solution.

Answer 1

This can be easily done in PHP… For this you need two arrays and a two while loops.

This code will make a tree the way you wanted and for an undetermined depth and number of children.

Pastebin to the working code.

Using references, lets imagine everything is saved in an array $data with this structure: (id, comment, parent_id) where parent_id points to an id.

Code to build the tree.

$tree = array();
reset($data);
while (list($k, $v) = each($data))
    if (0 == ($pid = $v['parent_id']))
        $tree[$k] =& $data[$k]; else
        $data[$pid]['children'][$k] =& $data[$k];

And to generate the depth and child count.

reset($data);
while (list($k, $v) = each($data))
    if (0 != $v['parent_id'])
    {
        $ref =& $data[$k];
        $depth = 0;
        do
        {
            if ($depth) $ref =& $data[$ref['parent_id']];
            $dre =& $ref['depth'];
            if (!isset($dre) || $dre <= $depth) $dre =  $depth++;
            if (isset($ref['children']))
                $ref['child_count'] = count($ref['children']);
                else
            {   
                $ref['child_count'] = 0;
                $ref['children'] = null;
            }   
        }   
        while ($ref['parent_id']);
    }

All my code has been written on the fly and not even tested, so if there are any errors please forgive meeeeeeeee!!!!!!!!!!! ← Forget that, I tried it, fixed a couple of issues and now works perfectly.

Note

For this code to work, the index of every item has to be equal to its ID.

The array I used to try the code.

$data = array(
    '1' => array('id' => '1', 'comment' => 'a', 'parent_id' => 0),
    '2' => array('id' => '2', 'comment' => 'b', 'parent_id' => 0),
    '3' => array('id' => '3', 'comment' => 'c', 'parent_id' => 1),
    '4' => array('id' => '4', 'comment' => 'd', 'parent_id' => 1),
    '5' => array('id' => '5', 'comment' => 'e', 'parent_id' => 2),
    '6' => array('id' => '6', 'comment' => 'f', 'parent_id' => 2),
    '7' => array('id' => '7', 'comment' => 'g', 'parent_id' => 5),
    '8' => array('id' => '8', 'comment' => 'h', 'parent_id' => 7)
    );