Grouped operations (and more)

[valpesendorfer]

This PR came from improvement work done for pre-calculating SPIs and such for admin extractions.

Most notably this PR adds:

• computation of groups along time dimension
  • gammastd_grp for grouped SPIs, that can be calculated by passing an array with group indices to the .algo.spi accessor
  • mean_grp grouped means (accessible through algo.mean_grp accessor)
• a new accessor rolling that allows for rolling computations over a defined window. Currently, rolling.sum is implemented
• a fix for zonal.mean which prevented the definition of output datatype

[Kirill888]

why this change is necessary? don't see any matching call-site changes

[Kirill888]

ok, I see why. Usually this problem of passing extra args to dask graph is best done with functools.partial(my_func, **fixed_named_args_that_might_alias)

[valpesendorfer]

There were a couple of problems with the previous implementation:

• dtype is already a keyword to map_blocks, so the naming is ambiguous when passed in through the accessor (which could be done with functools.partial I suppose.
• second problem was numba: when passing in a dtype with string notation it would fail compiling. Not sure if that would have been solved by using functools.partial, but passing the object works fine

[valpesendorfer]

OK this is now ready to be merged.

Quick summary:

Additions

• computation of groups along time dimension
  • gammastd_grp for grouped SPIs, that can be calculated by passing an array with group indices to the .algo.spi accessor
  • mean_grp grouped means (accessible through algo.mean_grp accessor)
• a new accessor rolling that allows for rolling computations over a defined window. Currently, rolling.sum is implemented

Improvements

• better handling of nodata in SPI methods
• a fix for zonal.meanwhich prevented the definition of output datatype

Unrelated changes

• surface Dekad.ndays from hdc.algo.dekad.Dekad to the Period accessor of hdc.algo

[valpesendorfer]

Updated summary:

Additions

• computation of groups along time dimension
  • gammastd_grp for grouped SPIs, that can be calculated by passing an array with group indices to the .algo.spi accessor
  • mean_grp grouped means (accessible through algo.mean_grp accessor)
• a new accessor rolling that allows for rolling computations over a defined window. Currently, rolling.sum is implemented

Improvements

• better handling of nodata in SPI methods
• a fix for zonal.meanwhich prevented the definition of output datatype

Unrelated changes

• surface from hdc.algo.dekad.Dekad to the Period accessor of hdc.algo:
  • Dekad.ndays
  • Dekad.start_date
  • Dekad.end_date
  • Dekad.raw