issue_comments: 378125383

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https://github.com/pydata/xarray/issues/2035#issuecomment-378125383 https://api.github.com/repos/pydata/xarray/issues/2035 378125383 MDEyOklzc3VlQ29tbWVudDM3ODEyNTM4Mw== 1217238 2018-04-03T04:33:40Z 2018-04-03T04:33:40Z MEMBER

If you look at the coordinates, the first and last labels get removed in arithmetic (by default we use an inner join).

You might find it more informative to look at the result of doing arithmetic with an outer join, which does result in some NaNs: ``` In [5]: with xr.set_options(arithmetic_join='outer'): ...: print(da[...,1:]-da[...,:-1]) ...: <xarray.DataArray (x: 5, y: 5, z: 5)> array([[[nan, 0., 0., 0., nan], [nan, 0., 0., 0., nan], [nan, 0., 0., 0., nan], [nan, 0., 0., 0., nan], [nan, 0., 0., 0., nan]],

   [[nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan]],

   [[nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan]],

   [[nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan]],

   [[nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan],
    [nan,  0.,  0.,  0., nan]]])

Coordinates: * z (z) int64 0 1 2 3 4 * x (x) int64 0 1 2 3 4 * y (y) int64 0 1 2 3 4 ```

 
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