Question

I have the following code (I know that this code is not optimized but it’s not for discussion):

function select_categories($cat_id)
{
    $this->db = ORM::factory('category')
            ->where('parent', '=', $cat_id)
            ->find_all();

    foreach ($this->db as $num => $category)
    {
        if($category->parent == 0)
        {
            $this->tmp[$category->parent][$category->id] = array();
        }
        else {
            $this->tmp[$category->parent][$category->id] = array();
        }

        $this->select_categories($category->id);
    }

    return $this->tmp;
}

Function returns this array:

array(3) (
    0 => array(2) (
        1 => array(0) 
        2 => array(0) 
    )
    2 => array(1) (
        3 => array(0) 
    )
    3 => array(2) (
        4 => array(0) 
        5 => array(0) 
    )
)

But how should I change the code

else {
    $this->tmp[$category->parent][$category->id] = array();
        // ^^^^^^^^^^^^^^^^^^^^^^ (this bit)
}

To merge array[3] to array[2][3] for example (because array[3] is a subdirectory of array[2] and array[2] is a subdirectory of array[0][2]), so, I need to make this (when I don’t know the level of subdirectories):

array (
    0 => array (
        1 => array 
        2 => array (
                    3 => array (
                                4 => array
                                5 => array
                                ) 
                    ) 
    ) 
)

Answer 1

Assuming you dont want any data/children tags in your array:

foreach ($this->db as $num => $category)
{
    // save the data to the array
    $this->tmp[$category->id] = array();

    // save a reference to this item in the parent array
    $this->tmp[$category->parent][$category->id] = &$this->tmp[$category->id];

    $this->select_categories($category->id);
}

// the tree is at index $cat_id
return $this->tmp[$cat_id];

If you just need to retrieve the full tree out of the database, you can even simplify your query (get all records at once) and remove the recursive call in this function. You will need an extra check that will only set the $this->tmp[$catagory->id] when it does not exist and else it should merge the data with the existing data.