I have a correct list of 252 rooms and check if there are some Revit elements inside. This gives me a list with true or false (as child of the rooms) for each element.
Now I need to know the index of every “true” in the sublists. So I use List.Map along with List.AllIndicesOf. This gives a list with only 246 items instead of the 252 rooms I really have in the list!
I marked it in my screenshot.
List.AllIndicesOf skipped the first 6 items from my original list. List.IndexOf gives me the full 252 items but this node is limited to 1 item per list.