Think i know whats going on…
Timeddf = @linq dfData |>
groupby(:ID) |>
transform(Trailing12 = running(prod, (:Growth .+1), 12).-1)
the 12 in there, there are ID categories that only have up to 10 rows, so it gets broken the moment it tries to do 12 passes where only 10 rows exist for the groupby category.
Hmmm… is there a simple way to tell it to ignore those? alternatively I guess i can filter out original df to ensure those dont occur.