issues: 630062936

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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
630062936 MDU6SXNzdWU2MzAwNjI5MzY= 4120 coarsen deletes attrs on original object 2448579 closed 0     13 2020-06-03T14:50:16Z 2020-09-09T19:30:42Z 2020-09-09T18:56:36Z MEMBER      

MCVE Code Sample

```python

Your code here

import xarray as xr

ds = xr.tutorial.load_dataset("air_temperature") ds2 = xr.tutorial.load_dataset("air_temperature")

xr.testing.assert_identical(ds, ds2) # passes ds.coarsen(lat=5).mean() xr.testing.assert_identical(ds, ds2) # fails ```

Bug: coarsen reductions are modifying the original dataset by deleting all attributes

``` AssertionErrorTraceback (most recent call last) <ipython-input-21-b0a179f01c99> in <module> 48 xr.testing.assert_identical(ds, ds2) 49 ds.coarsen(lat=5).mean() ---> 50 xr.testing.assert_identical(ds, ds2)

~/work/python/xarray/xarray/testing.py in assert_identical(a, b) 87 assert a.identical(b), formatting.diff_array_repr(a, b, "identical") 88 elif isinstance(a, (Dataset, Variable)): ---> 89 assert a.identical(b), formatting.diff_dataset_repr(a, b, "identical") 90 else: 91 raise TypeError("{} not supported by assertion comparison".format(type(a)))

AssertionError: Left and right Dataset objects are not identical

Differing coordinates: L * lat (lat) float32 75.0 72.5 70.0 67.5 65.0 ... 25.0 22.5 20.0 17.5 15.0 R * lat (lat) float32 75.0 72.5 70.0 67.5 65.0 ... 25.0 22.5 20.0 17.5 15.0 standard_name: latitude long_name: Latitude units: degrees_north axis: Y Differing data variables: L air (time, lat, lon) float32 241.2 242.5 243.5 ... 296.49 296.19 295.69 R air (time, lat, lon) float32 241.2 242.5 243.5 ... 296.49 296.19 295.69 long_name: 4xDaily Air temperature at sigma level 995 units: degK precision: 2 GRIB_id: 11 GRIB_name: TMP var_desc: Air temperature dataset: NMC Reanalysis level_desc: Surface statistic: Individual Obs parent_stat: Other actual_range: [185.16 322.1 ] ```

 
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   completed 13221727 issue

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