cftime-manipulation methods

[aulemahal]

At xclim, we implemented some methods for dealing with cftime arrays in xarray. I was wondering if any of this could be of interest for cf-xarray? We are planning to add cf-xarray as a dependency in the near future, so moving some functionality over here would make sense for everyone.

The two functions that could be interesting:

• xclim.core.calendar.convert_calendar, it converts datetime variables to other calendars, handling missing days and stuff like that. It could be made available as ds.time.cf.convert_calendar or simply as an helper I guess.
• xclim.core.calender.interp_calendar, same but instead of converting dates it interpolates data on a yearly basis. This might be too narrow for cf-xarray, because it only makes sense on data coarser than daily.

[dcherian]

These look awesome!

I would ask over at xarray if people are interested in adding some of this stuff. interp_calendar could go in interp for example. convert_calendar may be a little out of scope of xarray, so we could add that here. date_range could make sense in xarray etc...

What doesn't go in xarray can go here.