Recursive function to generate multidimensional array from database result

Question

I\'m looking to write a function that takes an array of pages/categories (from a flat database result) and generates an array of nested page/category items based on the pare

Answer 1

I know this question is old, but I Was facing a very similar problem - except with a very large amount of data. After some struggle, I managed to build the tree in one pass of the resultset - using references. This code is not pretty, but it works and it works quite fast. It's non-recursive - that is, there's only one pass over the resultset and then one array_filter at the end:

$dbh = new PDO(CONNECT_STRING, USERNAME, PASSWORD);
$dbs = $dbh->query("SELECT n_id, n_parent_id from test_table order by n_parent_id, n_id");
$elems = array();

while(($row = $dbs->fetch(PDO::FETCH_ASSOC)) !== FALSE) {
    $row['children'] = array();
    $vn = "row" . $row['n_id'];
    ${$vn} = $row;
    if(!is_null($row['n_parent_id'])) {
        $vp = "parent" . $row['n_parent_id'];
        if(isset($data[$row['n_parent_id']])) {
            ${$vp} = $data[$row['n_parent_id']];
        }
        else {
            ${$vp} = array('n_id' => $row['n_parent_id'], 'n_parent_id' => null, 'children' => array());
            $data[$row['n_parent_id']] = &${$vp};
        }
        ${$vp}['children'][] = &${$vn};
        $data[$row['n_parent_id']] = ${$vp};
    }
    $data[$row['n_id']] = &${$vn};
}
$dbs->closeCursor();

$result = array_filter($data, function($elem) { return is_null($elem['n_parent_id']); });
print_r($result);

When executed on this data:

mysql> select * from test_table;
+------+-------------+
| n_id | n_parent_id |
+------+-------------+
|    1 |        NULL |
|    2 |        NULL |
|    3 |           1 |
|    4 |           1 |
|    5 |           2 |
|    6 |           2 |
|    7 |           5 |
|    8 |           5 |
+------+-------------+

The last print_r produces this output:

Array
(
    [1] => Array
        (
            [n_id] => 1
            [n_parent_id] => 
            [children] => Array
                (
                    [3] => Array
                        (
                            [n_id] => 3
                            [n_parent_id] => 1
                            [children] => Array
                                (
                                )

                        )

                    [4] => Array
                        (
                            [n_id] => 4
                            [n_parent_id] => 1
                            [children] => Array
                                (
                                )

                        )

                )

        )

    [2] => Array
        (
            [n_id] => 2
            [n_parent_id] => 
            [children] => Array
                (
                    [5] => Array
                        (
                            [n_id] => 5
                            [n_parent_id] => 2
                            [children] => Array
                                (
                                    [7] => Array
                                        (
                                            [n_id] => 7
                                            [n_parent_id] => 5
                                            [children] => Array
                                                (
                                                )

                                        )

                                    [8] => Array
                                        (
                                            [n_id] => 8
                                            [n_parent_id] => 5
                                            [children] => Array
                                                (
                                                )

                                        )

                                )

                        )

                    [6] => Array
                        (
                            [n_id] => 6
                            [n_parent_id] => 2
                            [children] => Array
                                (
                                )

                        )

                )

        )

)

Which is exactly what I was looking for.