so to answer your question from tnb ...i'm tempted to just tell you but this might be a good exercise in searching the atoms reference, which is a very important skill for jelly
in a case like this, it's a very easy search, but sometimes it takes a few tries (like when you've got some "split" builtins and some "partition" builtins and you're not sure which it is you're looking for)
hmm... I was thinking about using a list [1,2,3,...,365] and splitting it, but that will not work, since the dates are independent of the year, eg Q1 does not start on the first of January. This was sort of what I was going to do: 365Rṣ but that wont work because of the above
@NewPosts I have a hacked together 13 byte Jelly answer. I'm sure there is an elegant solution to this in Jelly, and am offering a bounty of at least +50 (maybe more if I really like it) for such an elegant solution (I'll be the judge of "elegant", but generally, it should be single digit length)