Nested object list items filtered & repeated

In my app I want to have a list of data that is unique. That data setup is a lsit of objects with a list of objects in it:

-id
-date
-note
-symptom (=list of objects)
– id
– tag

What I need is a list of all “tag” items and only unique ones.

I have a repeat within a repeat set up on my page, but I do not know how to get that data in. Is there a MAP function setup and filter for uniqueness that I can use with a page variable?

Thank you for your help.