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
58117200,MDU6SXNzdWU1ODExNzIwMA==,324,Support multi-dimensional grouped operations and group_over,1217238,open,0,,741199,12,2015-02-18T19:42:20Z,2022-02-28T19:03:17Z,,MEMBER,,,,"Multi-dimensional grouped operations should be relatively straightforward -- the main complexity will be writing an N-dimensional concat that doesn't involve repetitively copying data.

The idea with `group_over` would be to support groupby operations that act on a single element from each of the given groups, rather than the unique values. For example, `ds.group_over(['lat', 'lon'])` would let you iterate over or apply to 2D slices of `ds`, no matter how many dimensions it has.

Roughly speaking (it's a little more complex for the case of non-dimension variables), `ds.group_over(dims)` would get translated into `ds.groupby([d for d in ds.dims if d not in dims])`. 

Related: #266
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