递归函数从分层数组生成平面（但带有标题嵌套）数组

Question

Another recursion question.

What I've tried to develop for the past few hours is a function that will let me generate a flat array of the same pages, but with the children having an identifier in front of them, (i.e. "— Sub Page, — — Sub Sub Page, etc").

I have a hierarchical array of pages, with each child page nested inside of their parent page. Here's an example of their output:

Array
(
    [0] => Array
        (
            [id] => 1
            [parent_id] => 0
            [title] => Parent Page
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 12
                            [parent_id] => 1
                            [title] => Another Sub Page
                        )

                    [1] => Array
                        (
                            [id] => 3
                            [parent_id] => 1
                            [title] => Sub Page
                            [children] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 7
                                            [parent_id] => 3
                                            [title] => Sub Sub Page
                                        )

                                )

                        )

                )

        )

    [1] => Array
        (
            [id] => 8
            [parent_id] => 0
            [title] => Another Parent Page
        )

)

I've been able to get it working until I reach the second level of the recursion and then it's still generating only one —. I want to make the solution recursive.

What I'm looking for in the final output using the example above is:

Array
(
    [1] => Parent Page
    [12] => — Another Sub Page
    [3] => — Sub Page
    [7] => — — Sub Sub Page
    [8] => Another Parent Page
)

Answer 1

function generate_array(array $arr, &$output = array(), $index = 0)
{
    foreach($arr as $item)
    {
        $output[$item['id']] = str_repeat('— ', $index) . $item['title'];
        if(isset($item['children']))
        {
            generate_array($item['children'], $output, $index + 1);
        }
    }
    return $output;
}

$output = generate_array($arr);

The data stored in $output would be:

Array
(
    [1] =>  Parent Page
    [12] => — Another Sub Page
    [3] => — Sub Page
    [7] => — — Sub Sub Page
    [8] =>  Another Parent Page
)