issues: 349857086

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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
349857086 MDU6SXNzdWUzNDk4NTcwODY= 2363 Reduction APIs for groupby, groupby_bins, resample, rolling 6815844 closed 0     1 2018-08-13T00:30:10Z 2018-09-28T06:54:30Z 2018-09-28T06:54:30Z MEMBER      

From #2356

APIs for groupby, groupby_bins, resample, rolling are different, especially for multi-dimensional array.

```python import numpy as np import xarray as xr import pandas as pd

time = pd.date_range('2000-01-01', freq='6H', periods=365 * 4) ds = xr.Dataset({'foo': (('time', 'x'), np.random.randn(365 * 4, 5)), 'time': time, 'x': [0, 1, 2, 1, 0]})

ds.rolling(time=2).mean() # result dims : ('time', 'x') ds.resample(time='M').mean() # result dims : ('time', 'x') ds['foo'].resample(time='M').mean() # result dims : ('time', ) maybe a bug #2362 ds.groupby('time.month').mean() # result dims : ('month', ) ds.groupby_bins('time', 3).mean() # result dims : ('time_bins', ) ```

  • In rolling and resample(for Dataset), reduction without argument is carried out along grouped dimension
  • In rolling, reduction along other dimesnion is not possible
  • In groupby and groupby_bins, reduction is applied to the grouped objects and if without argument, it reduces alongall the dimensions of each grouped object.

I think rollings API is most clean, but I am not sure it is worth to change these APIs.

The possible options would be 1. Change APIs of groupby and groupby_bins so that they share similar API with rolling. 2. Document clearly how to perform resample or groupby with multidimensional arrays.

 
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