html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1217#issuecomment-273544152,https://api.github.com/repos/pydata/xarray/issues/1217,273544152,MDEyOklzc3VlQ29tbWVudDI3MzU0NDE1Mg==,10050469,2017-01-18T17:34:13Z,2017-01-18T17:34:13Z,MEMBER,"> . So in my case extracting the data with the shared dimension using ds.drop() is appropriate. It would be nice to have xarray throw a warning or error to prevent me chomping up all the RAM in my system if I do try to do this sort of thing though. 

I'll let @shoyer give a definitive answer here, but I don't think that ``.where`` is meant to check whether the input makes ""sense"" or not. What happens is related to how xarray chooses to broadcast non matching dimensions:

```python
import xarray as xr
import numpy as np
d1 = xr.DataArray(np.arange(3), coords={'t1': np.linspace(0, 1, 3)}, dims='t1')
d2 = xr.DataArray(np.arange(4), coords={'t2': np.linspace(0, 1, 4)}, dims='t2')

d2 * d1
<xarray.DataArray (t2: 4, t1: 3)>
array([[0, 0, 0],
       [0, 1, 2],
       [0, 2, 4],
       [0, 3, 6]])
Coordinates:
  * t2       (t2) float64 0.0 0.3333 0.6667 1.0
  * t1       (t1) float64 0.0 0.5 1.0

d2.where(d1 == 1)
<xarray.DataArray (t2: 4, t1: 3)>
array([[ nan,   0.,  nan],
       [ nan,   1.,  nan],
       [ nan,   2.,  nan],
       [ nan,   3.,  nan]])
Coordinates:
  * t2       (t2) float64 0.0 0.3333 0.6667 1.0
  * t1       (t1) float64 0.0 0.5 1.0
```
which ""makes sense"", but is going to have a huge memory consumption if your arrays are large. 
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,201617371
https://github.com/pydata/xarray/issues/1217#issuecomment-273520435,https://api.github.com/repos/pydata/xarray/issues/1217,273520435,MDEyOklzc3VlQ29tbWVudDI3MzUyMDQzNQ==,10050469,2017-01-18T16:14:19Z,2017-01-18T16:14:19Z,MEMBER,"Thanks for the report! It would be great if you could be a bit more specific:
- if data1 and data2 are unrelated, why do you want to apply ``where`` on both variables? What is your expectation on the output?
- do you have the possibility to produce a minimal, self-contained working example?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,201617371