How to display certain sections and elements nested in them using ORM Bitrix?

Question

1C-Bitrix

The task is to display certain sections and the elements located in them using Bitrix ORM in the following form:
Section name 1

1. Document 1
   
2. Document 2
   

Section name N

1. Document N
   
2. Document N
   

Conditions - One element can be in different sections. The level of nesting of sections can be different. It is desirable to execute selection from a DB for one request.

Implementation
We use ORM Bitrix

use \Bitrix\Main\Loader;
Loader::includeModule('iblock');

$iblockId = 7; // ID Инфоблока 
$sections = array(298, 4);  // ID необходимых разделов
$elementId = 29; // ID элемента - для проверки в каких разделах состоит элемент

// API инфоблока - Docs 
// Попробуем реализовать через getList
$elements = \Bitrix\Iblock\Elements\ElementDocsTable::getList([
    // Чтобы получить все разделы элемента, в select указываем SECTIONS
    // Из SECTIONS выберем только ID, NAME и добавим алиасы SECTION_
    'select' => ['ID', 'NAME', 'IBLOCK_ID', 'SECTION_ID'=>'SECTIONS.ID', 'SECTION_NAME'=>'SECTIONS.NAME'],
    'filter' => [
        'IBLOCK_ID' => $iblockId, // ID инфоблока
        'SECTIONS.ID' => $sections, // ID необходимых разделов
        // 'ID' => $elementId, // Для проверки в каких разделах состоит элемент
    ],
    'limit' => '20', // Количество элементов
])->fetchAll();

As a result, we get the following array
One element with 'ID' => 29 consists of two sections, with different levels of nesting. The keys in the array are 0 and 2.

Array(
    [0] => Array
        (
            [ID] => 29
            [NAME] => Федеральный закон от 25.12.2008 №273-ФЗ "О противодействии коррупции"
            [IBLOCK_ID] => 7
            [SECTION_ID] => 4
            [SECTION_NAME] => Противодействие коррупции
        )
    [1] =>  Array
        (
            [ID] => 36
            [NAME] => Положение о комиссии по урегулированию споров и предотвращению конфликта интересов
            [IBLOCK_ID] => 7
            [SECTION_ID] => 4
            [SECTION_NAME] => Противодействие коррупции
        )
    [2] => Array
        (
            [ID] => 29
            [NAME] => Федеральный закон от 25.12.2008 №273-ФЗ "О противодействии коррупции"
            [IBLOCK_ID] => 7
            [SECTION_ID] => 298
            [SECTION_NAME] => Архив
        )
    [3] => Array
        (
            [ID] => 29
            [NAME] => Постановление правительства от 05.07.2013 №568 "О распространении ограничений"
            [IBLOCK_ID] => 7
            [SECTION_ID] => 298
            [SECTION_NAME] => Архив
        )
)

Question - How to form the result of $elements into an array of the following form?
It is desirable to write the implementation in the answer.

Array
(
    [0] => Array
        (
            [SECTION_ID] => 29
            [SECTION_NAME] => Раздел 1
            [ELEMENTS] => Array
                (
                    [0] => Array
                        (
                            [ID] => 11
                            [ELEMENT_NAME] => Документ 1
                        )

                    [1] => Array
                        (
                            [ID] => 223
                            [ELEMENT_NAME] => Документ 2
                        )

                )

        )

    [1] => Array
        (
            [SECTION_ID] => 30
            [SECTION_NAME] => Раздел N
            [ELEMENTS] => Array
                (
                    [0] => Array
                        (
                            [ID] => 44
                            [ELEMENT_NAME] => Документ N
                        )

                    [1] => Array
                        (
                            [ID] => 323
                            [ELEMENT_NAME] => Документ N
                        )

                )

        )
)

Answer 1

while ($element = $elements->fetch())
{
  $sectionId = $element['SECTION_ID'];

  $result[$sectionId] = [
    'SECTION_ID' => $sectionId,
    'SECTION_NAME' => $element['SECTION_NAME'],
  ];

  $result[$sectionId]['ELEMENTS'][] = [
    'ID' => $element['ID'],
    'ELEMENT_NAME' => $element['NAME'],
  ];
}