Create list of Wall Types (Don't show duplicates)

Let me start by saying I am VERY new to Dynamo and have been reading a ton to try and learn some things. I took another Dynamo Script and am trying to modify it a bit to suit my needs.
I am trying to have Dynamo scan my project and give me a list (Excel file) of all of the different wall types. It currently gives me a list of EVERY INSTANCE of ALL wall types placed in project. So if wall type 4A has 100 instances, 4B has 25 instances, 4C has 50 instances, etc and my excel file list them all and I just want each to be listed once. I have a feeling it needs “AllIndicesOf” somewhere, but I can’t get that to work…any help would be much appreciated.

I’ve posted my script for reference.

I just finished training people today and got a question about that specific thing.
Lucky you
you can do it like so: