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/3068#issuecomment-508862961,https://api.github.com/repos/pydata/xarray/issues/3068,508862961,MDEyOklzc3VlQ29tbWVudDUwODg2Mjk2MQ==,1828519,2019-07-05T21:10:50Z,2019-07-05T21:10:50Z,CONTRIBUTOR,"Ah, good call. The `transpose` currently in xarray would still be a problem though.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,462859457
https://github.com/pydata/xarray/issues/3068#issuecomment-507656176,https://api.github.com/repos/pydata/xarray/issues/3068,507656176,MDEyOklzc3VlQ29tbWVudDUwNzY1NjE3Ng==,1828519,2019-07-02T12:31:54Z,2019-07-02T12:33:15Z,CONTRIBUTOR,"@shoyer Understood. That explains why something like this wasn't caught before, but what would be the best solution for a short term fix?

For the long term, I also understand that there isn't really a good way to check equality of two dask arrays. I wonder if dask's graph optimization could be used to ""simplify"" two dask arrays' graph separately and check the graph equality. For example, two dask arrays created by doing `da.zeros((10, 10), chunks=2) + 5` should be theoretically equal because their dask graphs are made up of the same tasks.

Edit: ""short term fix"": What is the best way to avoid the unnecessary transpose? Or is this not even the right way to approach this? Change dask to avoid the unnecessary transpose or change xarray to not do the tranpose or something else?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,462859457
https://github.com/pydata/xarray/issues/3068#issuecomment-507410467,https://api.github.com/repos/pydata/xarray/issues/3068,507410467,MDEyOklzc3VlQ29tbWVudDUwNzQxMDQ2Nw==,1828519,2019-07-01T20:20:05Z,2019-07-01T20:20:05Z,CONTRIBUTOR,"Modifying [this line](https://github.com/pydata/xarray/blob/master/xarray/core/variable.py#L1223) to be:

```python
if dims == expanded_vars.sizes:
    return expanded_vars
return expanded_var.transpose(*dims)
```

Then this issue is avoided for at least the `+` case.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,462859457
https://github.com/pydata/xarray/issues/3068#issuecomment-507405717,https://api.github.com/repos/pydata/xarray/issues/3068,507405717,MDEyOklzc3VlQ29tbWVudDUwNzQwNTcxNw==,1828519,2019-07-01T20:05:51Z,2019-07-01T20:05:51Z,CONTRIBUTOR,"Ok another update. In the previous example I accidentally added the `lons` coordinate DataArray with the dimensions redefined `(('y', 'x'), lons2)` which is technically redundant but it worked (no progress bar).

However, if I fix this redundancy and do:

```python
a = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'lons': lons2})
b = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'lons': lons2})
with ProgressBar():
    c = a + b
```

I **do** get a progress bar again (lons2 is being computed). I've tracked it down to this `transpose` which is transposing when it doesn't need to which is causing the dask array to change:

https://github.com/pydata/xarray/blob/master/xarray/core/variable.py#L1223

I'm not sure if this would be considered a bug in dask or xarray. Also, not sure why the redundant version of the example worked.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,462859457
https://github.com/pydata/xarray/issues/3068#issuecomment-507396912,https://api.github.com/repos/pydata/xarray/issues/3068,507396912,MDEyOklzc3VlQ29tbWVudDUwNzM5NjkxMg==,1828519,2019-07-01T19:38:06Z,2019-07-01T19:38:06Z,CONTRIBUTOR,"Ok I'm getting a little more of an understanding on this. The main issue is that the dask array is not literally considered the same object because I'm creating the object twice. If I create a single dask array and pass it:

```python
lons = da.zeros((10, 10), chunks=2)
a = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'y': np.arange(10), 'x': np.arange(10), 'lons': (('y', 'x'), lons)})
b = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'y': np.arange(10), 'x': np.arange(10), 'lons': (('y', 'x'), lons)})
```

I still get the progress bar because xarray is creating two new `DataArray` objects for this `lons` coordinate. So `lons_data_arr.variable._data is not lons_data_arr2.variable._data` causing the equivalency check [here](https://github.com/pydata/xarray/blob/master/xarray/core/variable.py#L1495) to fail.

If I make a single DataArray that becomes the coordinate variable then it seems to work:

```python
lons2 = xr.DataArray(lons, dims=('y', 'x'))
a = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'y': np.arange(10), 'x': np.arange(10), 'lons': (('y', 'x'), lons2)})
b = xr.DataArray(da.zeros((10, 10), chunks=2), dims=('y', 'x'), coords={'y': np.arange(10), 'x': np.arange(10), 'lons': (('y', 'x'), lons2)})
```

I get no progress bar.
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,462859457