reindex in .unstack for pandas consistency

Author: shoyer

xray/core/dataset.py

@@ -1386,14 +1386,17 @@ def unstack(self, dim):
             raise ValueError('cannot unstack a dimension that does not have '
                              'a MultiIndex')
 
+        full_idx = pd.MultiIndex.from_product(index.levels, names=index.names)
+        obj = self.reindex(copy=False, **{dim: full_idx})
+
         new_dim_names = index.names
         if any(name is None for name in new_dim_names):
             raise ValueError('cannot unstack dimension with unnamed levels')
 
         new_dim_sizes = [lev.size for lev in index.levels]
 
         variables = OrderedDict()
-        for name, var in self.variables.items():
+        for name, var in obj.variables.items():
             if name != dim:
                 if dim in var.dims:
                     new_dims = OrderedDict(zip(new_dim_names, new_dim_sizes))

xray/test/test_dataarray.py

@@ -868,6 +868,15 @@ def test_stack_unstack(self):
         actual = orig.stack(z=['x', 'y']).unstack('z')
         self.assertDataArrayIdentical(orig, actual)
 
+    def test_unstack_pandas_consistency(self):
+        df = pd.DataFrame({'foo': range(3),
+                           'x': ['a', 'b', 'b'],
+                           'y': [0, 0, 1]})
+        s = df.set_index(['x', 'y'])['foo']
+        expected = DataArray(s.unstack(), name='foo')
+        actual = DataArray(s, dims='z').unstack('z')
+        self.assertDataArrayIdentical(expected, actual)
+
     def test_transpose(self):
         self.assertVariableEqual(self.dv.variable.transpose(),
                                  self.dv.transpose())