I am a new user, and my request doesn’t seem impossible. I created a temperature parameter in my spaces. Located my electrical fixtures within that space using Space.IsInSpace, as expected I got a list of all the spaces in the model, within each list (nested list) of TRUE & FALSE conditions. So far so good, I was seeking to extract the temperatures from my list of spaces, cross reference it with my fixture locations i.e. the TRUE or FALSE and use this further down the line to size my cables. For some reason, seems straight forward enough to me, but because its a nested list it is proving to be V troublesome. I can’t flatten it as I would lose all my mapping and the nodes out the box are giving me the run around. Has anyone had a similar problem and could shed some light on the subject?
Hello Davie - Welcome to the community! 
This sounds like a classic List Level challenge that can be a little harder to reconcile when starting your Dynamo journey. It would help if you are able to illustrate with screenshots or mock-ups the exact problem you are having, otherwise we’re flying a little blind.
But, based on what you are saying, here’s my best guess (Note I’m using Revit 2025 and Dynamo 3.2, but the logic should theoretically still stand in Revit 2021):
Inside this graph, note that the List.AllIndicesOf node uses cross-product lacing (Checking every Space against every Electrical Fixture).
Please replace the conditions, parameter names etc. as needed. Hopefully this logic helps!
Thanks @davie_henderson! Is the solution I posted above what you are looking for? Or does that not work for you?
Your work flow was a great help! Thanks very much mate!!
Ok awesome - glad it’s helping 