Request: implement unsigned integer type for xarray resample skipna

[mmartini-usgs]

I would like to be able to use the skipna switch with unsigned integer types in netCDF4 files I'm processing with xarray.

Currently it appears to be unsupported:

    184                 raise NotImplementedError(
    185                     'skipna=True not yet implemented for %s with dtype %s'
--> 186                     % (name, values.dtype))
    187             nanname = 'nan' + name
    188             if (isinstance(axis, tuple) or not values.dtype.isnative or

NotImplementedError: skipna=True not yet implemented for mean with dtype uint32

Thanks,
Marinna

[fujiisoup]

I first thought skipna=True does not make sense for uint array because NaN is a float, but I just noticed it would be inconvenient for Dataset containing float and uint.
Sent a PR.

[mmartini-usgs]

I'm generating netCDF4 files that have a variety of variables that have values representing things that are integer in nature and can't physically be negative. So to save space and provide as much bandwidth in the variable, I was careful to use float, int, unit types as appropriate. And then could not use resample with skipna because uint was not supported. I have gone back and made the uints into ints, skipna now works on my data, and I might now need to use 64 bit instead of 32 which defeats my efforts to keep the files as small as possible. It seems to me that if skipna is implemented for one or two types it should work for all of them.
It's also quite possible I've mistaken something - I'm an experienced programmer in C and MATLAB and very new to python and have learned the lard way that what's obvious in C or C++ is not so in python.