issues: 898657012

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
898657012 MDU6SXNzdWU4OTg2NTcwMTI= 5361 Inconsistent behavior in grouby depending on the dimension order 6815844 open 0     1 2021-05-21T23:11:37Z 2022-03-29T11:45:32Z   MEMBER      

groupby works inconsistently depending on the dimension order of a DataArray. Furthermore, in some cases, this causes a corrupted object.

python In [4]: data = xr.DataArray( ...: np.random.randn(4, 2), ...: dims=['x', 'z'], ...: coords={'x': ['a', 'b', 'a', 'c'], 'y': ('x', [0, 1, 0, 2])} ...: ) ...: ...: data.groupby('x').mean() Out[4]: <xarray.DataArray (x: 3, z: 2)> array([[ 0.95447186, -1.14467028], [ 0.76294958, 0.3751244 ], [-0.41030223, -1.35344548]]) Coordinates: * x (x) object 'a' 'b' 'c' Dimensions without coordinates: z groupby works fine (although this drops nondimensional coordinate y, related to #3745).

However, groupby does not give a correct result if we work on the second dimension, python In [5]: data.T.groupby('x').mean() # <--- change the dimension order, and do the same thing Out[5]: <xarray.DataArray (z: 2, x: 3)> array([[ 0.95447186, 0.76294958, -0.41030223], [-1.14467028, 0.3751244 , -1.35344548]]) Coordinates: * x (x) object 'a' 'b' 'c' y (x) int64 0 1 0 2 # <-- the size must be 3!! Dimensions without coordinates: z

The bug has been discussed in #2944 and solved, but I found this is still there.

Output of <tt>xr.show_versions()</tt> INSTALLED VERSIONS ------------------ commit: 09d8a4a785fa6521314924fd785740f2d13fb8ee python: 3.7.7 (default, Mar 23 2020, 22:36:06) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 5.4.0-72-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.10.4 libnetcdf: 4.6.1 xarray: 0.16.1.dev30+g1d3dee08.d20200808 pandas: 1.1.3 numpy: 1.18.1 scipy: 1.5.2 netCDF4: 1.4.2 pydap: None h5netcdf: 0.8.0 h5py: 2.10.0 Nio: None zarr: None cftime: 1.2.1 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.6.0 distributed: 2.7.0 matplotlib: 3.2.2 cartopy: None seaborn: 0.10.1 numbagg: None pint: None setuptools: 46.1.1.post20200323 pip: 20.0.2 conda: None pytest: 5.2.1 IPython: 7.13.0 sphinx: None 
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