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
159222357,MDU6SXNzdWUxNTkyMjIzNTc=,877,Bug in multiplying datasets? Removes coordinates for lats,9618134,closed,0,,,4,2016-06-08T17:10:52Z,2016-06-08T18:31:14Z,2016-06-08T18:31:14Z,NONE,,,,"I wasn't sure if this should go on the googlegroup or here, but the xarray docs says bugs go here so here it is.

I am doing a very simple operation. I have two netcdf files that I load in and then multiply. First:

``` Python
import xarray as xr
ncscd='NCSCDv2_Circumpolar_WGS84_SOCC30_05deg.nc'
ncscddata30 = xr.open_dataset(ncscd)
ncscd_d30cm = ncscddata30['NCSCDv2'].load()
print ncscd_d30cm


> xarray.DataArray 'NCSCDv2' (lat: 111, lon: 720)
array([[ nan,  nan,  nan, ...,  nan,  nan,  nan],
       [ nan,  nan,  nan, ...,  nan,  nan,  nan],
       [ nan,  nan,  nan, ...,  nan,  nan,  nan],
       ..., 
       [ nan,  nan,  nan, ...,  nan,  nan,  nan],
       [ nan,  nan,  nan, ...,  nan,  nan,  nan],
       [ nan,  nan,  nan, ...,  nan,  nan,  nan]])
Coordinates:
  * lon      (lon) float64 -179.7 -179.2 -178.7 -178.2 -177.7 -177.2 -176.7 ...
  * lat      (lat) float64 89.75 89.25 88.75 88.25 87.75 87.25 86.75 86.25 ...
Attributes:
    long_name: NCSCDv2
    esri_pe_string: GEOGCS[""GCS_WGS_1984"",DATUM[""D_WGS_1984"",SPHEROID[""WGS_1984"",6378137.0,298.257223563]],PRIMEM[""Greenwich"",0.0],UNIT[""Degree"",0.0174532925199433]]
    units: Degree
```

And then the second:

``` Python
gridfile ='NCSCDv2_gridarea.nc'
gridarea = xr.open_dataset(gridfile).load()
print gridarea

> xarray.Dataset
Dimensions:    (lat: 111, lon: 720)
Coordinates:
  * lon        (lon) float64 -179.7 -179.2 -178.7 -178.2 -177.7 -177.2 ...
  * lat        (lat) float64 89.75 89.25 88.75 88.25 87.75 87.25 86.75 86.25 ...
Data variables:
    cell_area  (lat, lon) float64 1.337e+07 1.337e+07 1.337e+07 1.337e+07 ...
Attributes:
    CDI: Climate Data Interface version 1.6.8 (http://mpimet.mpg.de/cdi)
    Conventions: CF-1.4
    history: Mon May 16 18:13:43 2016: cdo gridarea NCSCDv2_Circumpolar_WGS84_SOCC100_05deg.nc NCSCDv2_gridarea.nc
    CDO: Climate Data Operators version 1.6.8rc2 (http://mpimet.mpg.de/cdo)
```

Both arrays are the same size. Now I simply multiply them together but note that lats in the output are now 0.

``` Python
ncscd_total30cm = gridarea.cell_area * ncscd_d30cm
print ncscd_total30cm 

> xarray.Dataset
Dimensions:    (lat: 0, lon: 720)
Coordinates:
  * lat        (lat) float64 
  * lon        (lon) float64 -179.7 -179.2 -178.7 -178.2 -177.7 -177.2 ...
Data variables:
    cell_area  (lat, lon) float64 
Attributes:
    CDI: Climate Data Interface version 1.6.8 (http://mpimet.mpg.de/cdi)
    Conventions: CF-1.4
    history: Mon May 16 18:13:43 2016: cdo gridarea NCSCDv2_Circumpolar_WGS84_SOCC100_05deg.nc NCSCDv2_gridarea.nc
    CDO: Climate Data Operators version 1.6.8rc2 (http://mpimet.mpg.de/cdo)
```

This doesn't seem like it should be happening. Removing the .load() doesn't help. Bug?
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/877/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue
158785545,MDU6SXNzdWUxNTg3ODU1NDU=,871,Failing arithmetic operations with xarray.DataArray defined with chunks and lock=False,7727985,closed,0,,,2,2016-06-06T22:01:17Z,2016-06-08T18:10:52Z,2016-06-08T18:10:52Z,NONE,,,,"Trying to understand what was raising an exception with several methods associated to oocgcm grid objects that have been sliced ([see](https://github.com/lesommer/oocgcm/issues/33)), I have identified what I think might be an **issue when slicing xarray.DataArray defined with dask chunks + lock=False**. 

A illustration of the issue can be found [in this notebook](https://github.com/lesommer/notebooks/blob/master/Chunking_with_dask_problem.ipynb). I am afraid my understanding of xarray/dask is not sufficient for me to suggest a fix. 
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