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
571743567,MDExOlB1bGxSZXF1ZXN0MzgwNTc1NTYw,3801,Coarsen keep attrs 3376,29958771,closed,0,,,19,2020-02-27T00:29:13Z,2020-03-06T16:33:11Z,2020-03-02T23:02:56Z,CONTRIBUTOR,,0,pydata/xarray/pulls/3801,"<!-- Feel free to remove check-list items aren't relevant to your change -->

 - [x] Closes #3376
 - [x] Tests added
 - [x] Passes `isort -rc . && black . && mypy . && flake8`
 - [x] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API

I also noticed missing attributes when attempting certain operations, so I have created this pull request to attempt a fix. I modified code in `DataWithCoords.coarsen()` to try applying the same logic used for other methods since #2482 was successfully merged.

I added two new tests that adapt the bug reported by @jejjohnson. I believe they should pass when this is fixed. One uses `Dataset.coarsen()` and the other uses `Variable.coarsen`. Both tests currently fail.

xarray/tests/test_dataset.py::TestDataset::test_coarsen_keep_attrs 
- fails because my attempted fix does not retain the attributes.

xarray/tests/test_variable.py::TestVariable::test_coarsen_keep_attrs
- also fails, but unexpectedly this seems to be because the attributes are _not_ removed by default, or even when explicitly setting the global option to False. ","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/3801/reactions"", ""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
513975667,MDExOlB1bGxSZXF1ZXN0MzMzNjY1NDEw,3455,Update terminology.rst,29958771,closed,0,,,0,2019-10-29T14:49:00Z,2019-10-29T15:36:04Z,2019-10-29T15:36:04Z,CONTRIBUTOR,,0,pydata/xarray/pulls/3455,"Fixed broken link

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