PHP array_merge vs +, a case study on recursive array as tree

    private function extractSubCategories($categories)

    {

        $result = [];

        foreach ($categories as $key => $node) {

            if (empty($node['sub_categories'])) {

                $result[$node['id']] = $node;

            } else {

                $tmp = $node['sub_categories'];

                unset($node['sub_categories']);

                $result[$node['id']] = $node;

                $child = $this->extractSubCategories($tmp);

                $result = $result + $child;

            }

        }

        return $result;

    }

More detail ...

Damn it! Simple change array_merge to '+'

// Second way

        // foreach ($debug as $key => $node) {

        //     if (empty($node['sub_categories'])) {

        //         $result[$node['id']] = $node;

        //     } else {

        //         $secondStep = $secondStep + $node['sub_categories'];

        //     }

        // }

        // // dd($result);

        // dd($secondStep);

manually many steps.

        $debug = array_slice($data, 0, 7, true);

        // dd($debug);

        // echo '<pre>'. var_export($debug) . '</pre>';

        // $result = $this->extractSubCategories($debug);

slice($data, 0, 3, true) vs $data['1'] since its key retain.

JSON tree bonsai sample:

   "22":{

      "id":"22",

      "title":"OEM Rotor",

      "caption":"OEM Rotor",

      "parentId":"1",

      "sub_categories":[

         

      ],

      "childCount":0

   },

   "23":{

      "id":"23",

      "title":"Drilled Rotor",

      "caption":"Drilled Rotor",

      "parentId":"1",

      "sub_categories":[

      ],

      "childCount":0

   }
}

Code convert nested tree array to plain array (used for Bonsai JSON)

Recursive function;

    private function extractSubCategories($categories)

    {

        $result = [];

        foreach ($categories as $key => $node) {

            if (empty($node['sub_categories'])) {

                $result[$node['id']] = $node;

            } else {

                $tmp = $node['sub_categories'];

                unset($node['sub_categories']);

                $result[$node['id']] = $node;

                $child = $this->extractSubCategories($tmp);

                $result = $result + $child; // array_merge not work, it lost array keys 

            }

        }

        return $result;

    }

Nested PHP array look like:

Array
(
    [1] => Array
        (
            [id] => 1
            [title] => eLINE Brake Rotors
            [caption] => eLINE Series Brake Rotors
            [parentId] => 
            [sub_categories] => Array
                (
                    [22] => Array
                        (
                            [id] => 22
                            [title] => OEM Rotor
                            [caption] => OEM Rotor
                            [parentId] => 1
                            [sub_categories] => Array
                                (
                                )

                            [childCount] => 0
                        )

                    [23] => Array
                        (
                            [id] => 23
                            [title] => Drilled Rotor
                            [caption] => Drilled Rotor
                            [parentId] => 1
                            [sub_categories] => Array
                                (
                                )

                            [childCount] => 0
                        )
        )

...

)