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/1931#issuecomment-367456457,https://api.github.com/repos/pydata/xarray/issues/1931,367456457,MDEyOklzc3VlQ29tbWVudDM2NzQ1NjQ1Nw==,25473287,2018-02-21T20:13:29Z,2018-02-21T20:13:29Z,NONE,"@shoyer OK, I see that keeping the core dims does make sense in some cases. I am fine with doing something like

```
xr.apply_ufunc(apply_A, dr, 
               input_core_dims=[['x']], 
               output_core_dims=[['x_new']]).rename({'x_new': 'x'})
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,298834332
https://github.com/pydata/xarray/issues/1931#issuecomment-367380855,https://api.github.com/repos/pydata/xarray/issues/1931,367380855,MDEyOklzc3VlQ29tbWVudDM2NzM4MDg1NQ==,25473287,2018-02-21T16:17:44Z,2018-02-21T16:17:44Z,NONE,"@jhamman @rabernat Thanks for the help!

Raising an error when encountering this issue and adding `keep_core_coords=False` to optionally drop the coordinate would be a good solution for me. 

But is there any case that we do want to keep the core coordinate? Since `input_core_dims` means ""dimensions that should not be broadcast"", I suppose that the output DataArray has no way to inherit these non-broadcasting dimensions? Should the core coordinate just be dropped by default?

Another more basic issue: Users are allowed the mess-up the coordinate dimension of an existing DataArray. Is this an expected behavior?

```
In [1]: import xarray as xr

In [2]: xr.DataArray([0, 1, 2, 3], dims='x', coords={'x':[0, 1]}) # this is not allowed
(...)
ValueError: conflicting sizes for dimension 'x': length 4 on the data but length 2 on coordinate 'x'

In [3]: dr = xr.DataArray([0, 1, 2, 3], dims='x', coords={'x':[0, 1, 2, 3]})

In [4]: dr['x'] = [0, 1] # but you can mess-up the coordinate dimension afterwards

In [5]: dr
Out[5]:
<xarray.DataArray (x: 4)>
array([0, 1, 2, 3])
Coordinates:
  * x        (x) int64 0 1

In [6]: dr.to_netcdf('wrong_coordinate.nc')
(...)
ValueError: conflicting sizes for dimension 'x': length 4 on '__xarray_dataarray_variable__' and length 2 on 'x'
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,298834332