BUG fix +test .sel method gives error with float32 values

    .sel method gives error when it is used to select float32 values

    Resolves: #3137

xarray/core/dataset.py

@@ -1814,8 +1814,9 @@ def sel(self, indexers=None, method=None, tolerance=None, drop=False,
         DataArray.sel
         """
         indexers = either_dict_or_kwargs(indexers, indexers_kwargs, 'sel')
+        casted_indexers = self._maybe_cast_floats(indexers)
         pos_indexers, new_indexes = remap_label_indexers(
-            self, indexers=indexers, method=method, tolerance=tolerance)
+            self, indexers=casted_indexers, method=method, tolerance=tolerance)
         result = self.isel(indexers=pos_indexers, drop=drop)
         return result._overwrite_indexes(new_indexes)
 
@@ -2322,6 +2323,22 @@ def interp_like(self, other, method='linear', assume_sorted=False,
             ds = self.reindex(object_coords)
         return ds.interp(numeric_coords, method, assume_sorted, kwargs)
 
+    # Helper method for sel()
+    def _maybe_cast_floats(self, indexers):
+        """ Cast float labels passed to sel() method to the float
+        types of the corresponding coordinates"""
+        from .dataarray import DataArray
+        casted_indexers = indexers.copy()
+        for k, v in indexers.items():
+            coords_var = self.coords[k].values
+            if isinstance(indexers[k], (slice, DataArray, Variable)):
+                pass
+            elif (isinstance(coords_var, np.ndarray) and
+                  coords_var.dtype.kind == 'f'):
+                casting_type = getattr(coords_var.dtype, "type")
+                casted_indexers[k] = casting_type(indexers[k])
+        return casted_indexers
+
     # Helper methods for rename()
     def _rename_vars(self, name_dict, dims_dict):
         variables = OrderedDict()

xarray/tests/test_dataarray.py

@@ -817,6 +817,16 @@ def test_sel_dataarray_datetime(self):
         result = array.sel(delta=slice(array.delta[0], array.delta[-1]))
         assert_equal(result, array)
 
+    def test_sel_float32(self):
+        float_values = [0., 0.111, 0.222, 0.333]
+        coord_values = np.asarray(float_values, dtype='float32')
+        data_values = np.arange(4)
+        array = DataArray(data_values, [('float32_coord', coord_values)])
+        expected = DataArray(data_values[1:3], [('float32_coord',
+                                                 coord_values[1:3])])
+        actual = array.sel(float32_coord=float_values[1:3])
+        assert_equal(expected, actual)
+
     def test_sel_no_index(self):
         array = DataArray(np.arange(10), dims='x')
         assert_identical(array[0], array.sel(x=0))