Calendar: Julian

[DavisVaughan]

julian_year_month_day()
julian_year_month_weekday()

Using: https://github.com/r-lib/clock/blob/master/inst/include/date/julian.h

[jonthegeek]

Are you open to PRs to implement these? It would be a learning effort for me (working with cpp) but one I've wanted to take on.

[DavisVaughan]

Not quite yet, I may end up just doing this myself in the next clock release, but I also have a plan to clean up some of the clock internals and possibly change the internal format some, so i wouldn't want that to interfere with your pr. I appreciate it though!

[bbolker]

I'm very interested in this, but it feels like there are a lot of potential complications.

• Julian/Gregorian shift happened on different dates in different places. Is this something you're going to try to help the user with or will it be up to them to decide if Julian or Gregorian is relevant for a particular observation in their data?
• are you going to try to handle the shift of New Year's Day in various places (see here for example)?

Kerzhner, I. M. 1984. “Converting Dates from the Julian (Old Style) or French Republican (Revolutionary) Calendars to the Gregorian (New Style) Calendar.” Taxon 33 (3): 410–12. https://doi.org/10.2307/1220979.

PS the link to julian.h above is broken ...

[DavisVaughan]

Here's an updated link, not sure about all the particular details you mentioned yet https://github.com/HowardHinnant/date/blob/master/include/date/julian.h

[bbolker]

Thanks. It looks like it simply implements the calendar and allows conversion - doesn't tell you anything about dates. https://howardhinnant.github.io/date/julian.html I suspect it won't handle the New Year's Day/Lady Day shift correctly ...

[joeroe]

@bbolker The CRAN packages aion (for calendar dates) and era (for fractional years) support the Julian calendar, if it's any use.