数组中的类别层次结构（cat id => parent id）

Question

i am trying to create a multidimensional array hierarchy from a simple array which contains pairs of category ids and parent ids. The categories can be a parent and a subcategory at the same time. The base categories have a parent of 0 (=no parent). For example:

# cat_id => parent_id
$initialArray = array(
  1 => 0,
  2 => 1,
  3 => 2,

  4 => 0,
  5 => 4,

  6 => 0
);

From this, i'd like to get an array that represents a structure like this:

• 1
  • 2
    • 3
• 4
  • 5
• 6

I will not know the contents of $initialArray beforehand.

I tried to look at other similar questions but i couldn't find an answer. Please help!

Answer 1

Well it appears to me you need a recursive function. Assuming everything has a parent or value beginning at the base level of 0, I resituated the array to have all parent ids listing their children rather than the other way around above. After that, I created a recursive function.

$initialArray = array(
    1 => 0,
    2 => 1,
    3 => 2,

    4 => 0,
    5 => 4,

    6 => 0
);

// resituate the array
$parent_ids = array();
foreach ($initialArray as $category_id => $parent_id) {
    if (!isSet($parent_ids[$parent_id])) {
        $parent_ids[$parent_id] = array();
    }
    $parent_ids[$parent_id][] = $category_id;
}

// end_array is the result
$end_array = array();

/**
 * Takes the key of the parent, the current set that it's working off of, the list of parent ids for reference
 * and the current place in the end result array, acting recursively
 */
function recursive($parent_key, $current_set, $parent_ids, $end_array) {
    foreach ($current_set as $parent_value) {
        if (!isSet($parent_ids[$parent_value])) {
            $end_array[$parent_key][] = $parent_value;
        } else {
            // if the parent_value is found in parent_ids, pass those values to the same function and the current end_array position
            $end_array[$parent_key] = recursive($parent_value, $parent_ids[$parent_value], $parent_ids, $end_array[$parent_key]);
        }
    }
    return $end_array;
}
// start with the top most element
$end_array = recursive(key($parent_ids), current($parent_ids), $parent_ids, $end_array);

print '<pre>'.
    print_r($parent_ids, true).
    print_r($end_array,true).
    '</pre>'
;

Outputs:

// resituated array
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 4
            [2] => 6
        )

    [1] => Array
        (
            [0] => 2
        )

    [2] => Array
        (
            [0] => 3
        )

    [4] => Array
        (
            [0] => 5
        )

)

// the end result
Array
(
    [0] => Array
        (
            [1] => Array
                (
                    [2] => Array
                        (
                            [0] => 3
                        )

                )

            [4] => Array
                (
                    [0] => 5
                )

            [5] => 6
        )

)