I had a lot of trouble with this one. Mostly, because I don't use apps all that often, I have to admit that I cheated a little and still am a little unclear as to why I needed to do what I did. All the values I wanted in my drop-down needed to be headers. It seems there should be a way to filter a unique set of values as a list. I have to admit -- I am certainly being challenged and learning a lot.
Here's mine. Like several others have mentioned, it would be nice to be able to read values from a list directly into the drop down. I spent a lot of time trying to make this so it runs in one step as opposed to reading unique values from the db