I want to do sectioning when displaying table views based on NSSet.

This is my first time to ask a question.
It may be difficult to read, but please forgive me.

CoreData is trying to create a two-tier table view.

The data models are as follows:

·Main class
　Attribute Name, Category 1
　[Relationship] Details (Many)

·Detailed class
　Attribute Name, Category 2
　[Relationship] Main (1)

Table view in Tier 1 is the
automatically generated code.
in sectionNameKeyPath: on the NSFetchedResultsController I was able to divide it into sections by Category 1 of the main class.

Similarly, in Tier 2, I would like to section the detail class by Category 2.
I don't know how to handle the detail class obtained by NSSet from the main class.

I know how to sort it into NSArray, so
I can think of a simple way to loop and set it up, but

like NSFetchedResultsController in Tier 1 Please let me know if there is a way to make it into a two-dimensional array that is simply sectioned.