id,node_id,number,state,locked,title,user,body,created_at,updated_at,closed_at,merged_at,merge_commit_sha,assignee,milestone,draft,head,base,author_association,auto_merge,repo,url,merged_by
263538518,MDExOlB1bGxSZXF1ZXN0MjYzNTM4NTE4,2839,closed,0,Fixing deepcopy for Dataset.attrs,1277781,"<!-- Feel free to remove check-list items aren't relevant to your change -->

 - [x] Closes #2835
 - [X] Tests added
 - [X] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API
",2019-03-22T09:24:54Z,2019-03-30T03:14:38Z,2019-03-30T03:14:38Z,2019-03-30T03:14:38Z,7d0e895fc27482256804303a16827feafc828595,,,0,7c983e07cb48aaa710dcb71ffa6d725b7370b5e2,89dddc1f5892178abf7375e14adfd5b729b71037,CONTRIBUTOR,,13221727,https://github.com/pydata/xarray/pull/2839,
497372566,MDExOlB1bGxSZXF1ZXN0NDk3MzcyNTY2,4484,closed,0,xarray.map,1277781,"<!-- Feel free to remove check-list items aren't relevant to your change -->

UPDATE:
Please let me know whether this PR can be considered to be merged.
If not I won't bother trying to fix failed tests such as: 

> would reformat /home/vsts/work/1/s/xarray/core/map.py
> would reformat /home/vsts/work/1/s/xarray/core/dataset.py
> would reformat /home/vsts/work/1/s/xarray/tests/test_map.py
> Oh no! 💥 💔 💥

Thanks

--------
 - [x] Tests added
 - [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
 - [x] New functions/methods are listed in `api.rst`

I implemented the top-level xarray.map function.
It is a generalization of the Dataset.map method for those functions which take more than one DataArray as input.
The function will be applied to the intersection of the variables in the datasets.

E.g: 
```
f = lambda a, b: b-a
map([ds1, ds2], f)
```
More details in the docstring.

(I probably messed up something with git as the commits listed below also include my earlier commits not related to this PR. But the list of files is clean, it only includes what I'd like to merge)",2020-10-04T04:11:29Z,2023-10-16T18:54:19Z,2023-10-16T18:54:19Z,,34596731ec1e371d2f054939ace35acedc05ce16,,,0,d99b0d8a2e99724f3e403dc7426035ba4309f981,d1e4164f3961d7bbb3eb79037e96cae14f7182f8,CONTRIBUTOR,,13221727,https://github.com/pydata/xarray/pull/4484,