Magento 2 : what is the use of getFacetedData() in category filter?

Question

Magento 2 Category layered navigatoin,

In magento category layered navigation content comes from below file

vendor/magento/module-catalog-search/Model/Layer/Filter/Category.php

In this file, inside _getItemsData() function one line,

$optionsFacetedData = $productCollection->getFacetedData('category');

I want to know what is the use of getFacetedData('category') in magento.

Answer 1

getFacetedData only exists in the product "fulltext" collection,

i.e. for search results and category pages.

It returns information for the layered navigation, as returned by the search engine (MySQL).

For each of these, it contains the number of results like :

price ranges

categories

filterable attributes