I wonder why I don't find much information about this problem, which is not uncommon I think:
the parallelperiod-function counts always the number of days from the beginning of the period to get the value in the parallelperiod.
what if i have unequal periods, let's say i have 4 seasons every year, but they can start on different days and also can span different numbers of days. what possibilities are there to compare those seasons?
for example how can I solve the following requirement:
the parallel period of Date 2012-12-05 from Season 1 of year 2012 should give me the day 2011-12-05 from Season 1 of year 2011
if day 2011-12-05 was not part of season 1, parallel period should return 0.