Fix dim argument for isel_points/sel_points when it's a pandas.Index (#918)

Author: shoyer

doc/whats-new.rst

@@ -104,6 +104,9 @@ Bug fixes
 - Fixed incorrect test for dask version (:issue:`891`). By
   `Stephan Hoyer <https://github.com/shoyer>`_.
 
+- Fixed `dim` argument for `isel_points`/`sel_points` when a `pandas.Index` is
+  passed. By `Stephan Hoyer <https://github.com/shoyer>`_.
+
 - :py:func:`~xarray.plot.contour` now plots the correct number of contours
   (:issue:`866`). By `Fabien Maussion <https://github.com/fmaussion>`_.
 

xarray/core/dataset.py

@@ -1034,6 +1034,8 @@ def isel_points(self, dim='points', **indexers):
         Dataset.sel_points
         DataArray.isel_points
         """
+        from .dataarray import DataArray
+
         indexer_dims = set(indexers)
 
         def relevant_keys(mapping):
@@ -1072,10 +1074,9 @@ def relevant_keys(mapping):
                 # dim already exists
                 raise ValueError('Existing dimensions are not valid choices '
                                  'for the dim argument in sel_points')
-        else:
-            # try to cast dim to DataArray with name = points
-            from .dataarray import DataArray
-            dim = DataArray(dim, dims='points', name='points')
+
+        if not utils.is_scalar(dim) and not isinstance(dim, DataArray):
+            dim = as_variable(dim, key='points')
 
         # TODO: This would be sped up with vectorized indexing. This will
         # require dask to support pointwise indexing as well.

xarray/test/test_dataset.py

@@ -787,11 +787,18 @@ def test_isel_points(self):
         self.assertDataArrayIdentical(actual['station'].drop(['dim1', 'dim2']),
                                       stations['station'])
 
-        # make sure we get the default points coordinate when a list is passed
+        # make sure we get the default 'points' coordinate when a list is passed
         actual = data.isel_points(dim1=stations['dim1s'],
                                   dim2=stations['dim2s'],
                                   dim=['A', 'B', 'C'])
         assert 'points' in actual.coords
+        assert actual.coords['points'].values.tolist() == ['A', 'B', 'C']
+
+        # test index
+        actual = data.isel_points(dim1=stations['dim1s'].values,
+                                  dim2=stations['dim2s'].values,
+                                  dim=pd.Index(['A', 'B', 'C'], name='letters'))
+        assert 'letters' in actual.coords
 
         # can pass a numpy array
         data.isel_points(dim1=stations['dim1s'],