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
156857895,MDU6SXNzdWUxNTY4NTc4OTU=,861,Bug in arithmetic operations on DataArray objects whose dimensions are  numpy structured arrays or recarrays,5384661,closed,0,,,3,2016-05-25T21:46:38Z,2016-08-11T04:20:33Z,2016-08-11T04:20:33Z,CONTRIBUTOR,,,,"The following code will not run with current version of the xarray

```
import numpy as np
import xarray as xr
p_data = np.array([('John', 180), ('Stacy', 150), ('Dick',200)], dtype=[('name', '|S256'), ('height', int)])
p_data_1 = np.array([('John', 180), ('Stacy', 150), ('Dick',200)], dtype=[('name', '|S256'), ('height', int)])
weights_0 = xr.DataArray([80,56,120], dims=['participant'], coords={'participant':p_data})
weights_1 = xr.DataArray([81,52,115], dims=['participant'], coords={'participant':p_data_1})

print weights_1-weights_0
```

It will crash with the error 

`ValueError: index 'participant' not aligned`

The real cause is the `isnull` function from **pandas** that throws TypeError exception when called on e.g. numpy recarray or numpy structured array

A quick fix involves replacing `array_equiv` function in **xarray.core.ops.py** with the following implementation

```
def array_equiv(arr1, arr2):
    """"""Like np.array_equal, but also allows values to be NaN in both arrays
    """"""
    arr1, arr2 = as_like_arrays(arr1, arr2)
    if arr1.shape != arr2.shape:
        return False

    flag_array = (arr1 == arr2)

    # isnull fcn from pandas will throw TypeError when run on numpy structured array
    # therefore for dims that are np structured arrays we skip testing for nan
    try:

        flag_array |= (isnull(arr1) & isnull(arr2))

    except TypeError:
        pass

    return bool(flag_array.all())
```
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/861/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue