minor code clean up

xarray/core/dataset.py

@@ -2327,11 +2327,9 @@ def to_array(self, dim='variable', name=None):
 
     def _to_dataframe(self, ordered_dims):
         columns = [k for k in self if k not in self.dims]
-
-        index = self.coords.to_index(ordered_dims)
-
         data = [self._variables[k].set_dims(ordered_dims).values.reshape(-1)
                 for k in columns]
+        index = self.coords.to_index(ordered_dims)
         return pd.DataFrame(OrderedDict(zip(columns, data)), index=index)
 
     def to_dataframe(self):
@@ -2414,7 +2412,6 @@ def to_dask_dataframe(self, set_index=True):
 
         return df
 
-
     def to_dict(self):
         """
         Convert this dataset to a dictionary following xarray naming

xarray/tests/test_dask.py

@@ -16,7 +16,7 @@
 with suppress(ImportError):
     import dask
     import dask.array as da
-    import dask.dataframe
+    import dask.dataframe as dd
 
 
 class DaskTestCase(TestCase):
@@ -407,12 +407,12 @@ def test_to_dask_dataframe(self):
         expected_pd = pd.DataFrame(np.array([x, y]).T,
                                 columns=['a', 'b'],
                                 index=pd.Index(t, name='t'))
-        expected = dask.dataframe.from_pandas(expected_pd, chunksize=4)
+        expected = dd.from_pandas(expected_pd, chunksize=4)
 
         actual = ds.to_dask_dataframe()
 
         # test if we have dask dataframes
-        self.assertIsInstance(actual, dask.dataframe.DataFrame)
+        self.assertIsInstance(actual, dd.DataFrame)
 
         # use the .equals from pandas to check dataframes are equivalent
         assert expected.compute().equals(actual.compute()), (expected, actual)