I have sequences of transaction dates by buyer over a long period of time. To classify the buyers properly, I need three of those dates: the first date, the last date, and the penultimate (second to last) date. I can't use a List because of the 1,000 item max list size--there are buyers with more than 1,000 transaction dates.
I can use GROUPFIRST and GROUPLAST (side note: I am worried these are just convenience functions that are under-girded by a List. If true, GROUPLAST has a bug AFAIC). How can I get the second-to-last value in the sequence?
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