This module is the Drupal 8 Port for the Search API Grouping module. It allows you to group search results and denormalize entities when indexing them.

I have created two processors, one for the grouping part and the other is responsible for the denormalization.

With the grouping you're able to group the search result by a specific field. Inside the different groups it is possible to sort the results by another field ascending and descending. As well you can define how many results per group should be displayed.