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
203630267,MDU6SXNzdWUyMDM2MzAyNjc=,1234,`where` grows new dimensions for unrelated variables,500246,open,0,,,5,2017-01-27T13:02:34Z,2022-04-18T16:04:16Z,,CONTRIBUTOR,,,,"In the example below, the dimensionality for data variable `y` grows from `(b)` to `(b, a)` after calling the dataset `where` method.  This behaviour does not appear to be documented.  Is it a bug?

```
    In [46]: ds = xarray.Dataset({""x"": ((""a"", ""b""), arange(25).reshape(5,5)+100), ""y"": (""b"", arange(5)-100)}, {""a"": arange(5), ""b"": arange(5)*2, ""c"": ((""a"",), list(""ABCDE""))})
    
    In [47]: print(ds)
    <xarray.Dataset>
    Dimensions:  (a: 5, b: 5)
    Coordinates:
      * b        (b) int64 0 2 4 6 8
        c        (a) <U1 'A' 'B' 'C' 'D' 'E'
      * a        (a) int64 0 1 2 3 4
    Data variables:
        x        (a, b) int64 100 101 102 103 104 105 106 107 108 109 110 111 ...
        y        (b) int64 -100 -99 -98 -97 -96
    
    In [69]: ds.where((ds.c>='A') & (ds.c<='C'))
    Out[69]: 
    <xarray.Dataset>
    Dimensions:  (a: 5, b: 5)
    Coordinates:
      * b        (b) int64 0 2 4 6 8
        c        (a) <U1 'A' 'B' 'C' 'D' 'E'
      * a        (a) int64 0 1 2 3 4
    Data variables:
        x        (a, b) float64 100.0 101.0 102.0 103.0 104.0 105.0 106.0 107.0 ...
        y        (b, a) float64 -100.0 -100.0 -100.0 nan nan -99.0 -99.0 -99.0 ...
```
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