issue_comments: 242235696

@shoyer My 2 cents for how this might work after 0.8+ (auto-align during concat, merge and auto_combine goes a long to solving this already) is that the compat option of merge etc could have a 4th option 'nonnull_equals' (or better named...), with compatibility tested by e.g.

``` python import xarray.ufuncs as xrufuncs

def nonnull_compatible(first, second): """ Check whether two (aligned) datasets have any conflicting non-null values. """

# mask for where both objects are not null
both_not_null = xrufuncs.logical_not(first.isnull() | second.isnull())

# check remaining values are equal
return first.where(both_not_null).equals(second.where(both_not_null))

```

And then fillna to combine variables. Looking now I think this is very similar to what you are suggesting in #835.