Hi. Thanks so much for your assistance. This is definitely getting the results I was looking for. It is still syntacticallly more cumbersome than I might have hoped, but I can work with it. So I've got two follow questions/issues:
1) I can see there are many, more complex, options for aggregates, which I am trying to wrap my mind around. I'm wondering if any of these (esp. partial aggregates/combine functions, final functions or moving aggregates) could be used to streamline this into a single function call, or if that is barking up a dead tree.
2) I'm sure at this point I must be being dense, but after re-reading docs multiple times, I am still confused about one piece of this: