Remove groupby with multi-dimensional warning soon

[max-sixty]

MCVE Code Sample

We have a very verbose warning in 0.15: it prints on every groupby on an object with multidimensional coords.

So the notebook I'm currently working on has red sections like:

/home/mroos/.local/lib/python3.7/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray contains multi-dimensional coordinates. In the future, the dimension order of these coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims
/home/mroos/.local/lib/python3.7/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray contains multi-dimensional coordinates. In the future, the dimension order of these coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims
/home/mroos/.local/lib/python3.7/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray contains multi-dimensional coordinates. In the future, the dimension order of these coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims
/home/mroos/.local/lib/python3.7/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray contains multi-dimensional coordinates. In the future, the dimension order of these coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims
/home/mroos/.local/lib/python3.7/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray contains multi-dimensional coordinates. In the future, the dimension order of these coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims

Unless there's a way of reducing its verbosity (e.g. only print once per session?), let's aim to push the change through and remove the warning soon?

# Your code here
In [2]: import xarray as xr                                                                                                                                                                                                                                                                         

In [4]: import numpy as np        

In [16]: da = xr.DataArray(np.random.rand(2,3), dims=list('ab'))                                                                                                    

In [17]: da = da.assign_coords(foo=(('a','b'),np.random.rand(2,3)))                                                                                                 

In [18]: da.groupby('a').mean(...)                                                                                                                                  
[...]/python3.6/site-packages/xarray/core/common.py:664: FutureWarning: This DataArray 
contains multi-dimensional coordinates. In the future, the dimension order of these 
coordinates will be restored as well unless you specify restore_coord_dims=False.
  self, group, squeeze=squeeze, restore_coord_dims=restore_coord_dims
Out[18]: 
<xarray.DataArray (a: 2)>
array([0.59216558, 0.58616892])
Dimensions without coordinates: a

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.8 (default, Aug 7 2019, 17:28:10) [GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] python-bits: 64 OS: Linux OS-release: [...] machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.utf8 LOCALE: en_US.UTF-8 libhdf5: 1.10.4 libnetcdf: None

xarray: 0.15.0
pandas: 0.25.3
numpy: 1.18.1
scipy: 1.4.1
netCDF4: None
pydap: None
h5netcdf: None
h5py: 2.10.0
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: 3.1.2
cartopy: None
seaborn: 0.10.0
numbagg: None
setuptools: 45.0.0
pip: 20.0.2
conda: None
pytest: 5.3.2
IPython: 7.12.0
sphinx: 2.3.1