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
325439138,MDU6SXNzdWUzMjU0MzkxMzg=,2171,Support alignment/broadcasting with unlabeled dimensions of size 1,1217238,open,0,,,5,2018-05-22T19:52:21Z,2022-04-19T03:15:24Z,,MEMBER,,,,"Sometimes, it's convenient to include placeholder dimensions of size 1, which allows for removing any ambiguity related to the order of output dimensions.

Currently, this is not supported with xarray:
```
>>> xr.DataArray([1], dims='x') + xr.DataArray([1, 2, 3], dims='x')
ValueError: arguments without labels along dimension 'x' cannot be aligned because they have different dimension sizes: {1, 3}

>>> xr.Variable(('x',), [1]) + xr.Variable(('x',), [1, 2, 3])
ValueError: operands cannot be broadcast together with mismatched lengths for dimension 'x': (1, 3)
```

However, these operations aren't really ambiguous. With size 1 dimensions, we could logically do broadcasting like NumPy arrays, e.g.,
```
>>> np.array([1]) + np.array([1, 2, 3])
array([2, 3, 4])
```

This would be particularly convenient if we add `keepdims=True` to xarray operations (#2170).","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/2171/reactions"", ""total_count"": 4, ""+1"": 4, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue