Update filter_by_attrs to use 'variables' instead of 'data_vars' (#3247)

* Update filter_by_attrs to use 'variables' instead of 'data_vars'

This will allow `filter_by_attrs` to filter coordinates as well as variables. @ocefpaf

* added tests for filter_by_attrs acting on coords

* fixed pep8 issues

* Change standard_name to long_name in filter_by_attrs test

* remove whitespace

Author: cspencerjones

xarray/core/dataset.py

@@ -5148,7 +5148,7 @@ def filter_by_attrs(self, **kwargs):
 
         """  # noqa
         selection = []
-        for var_name, variable in self.data_vars.items():
+        for var_name, variable in self.variables.items():
             has_value_flag = False
             for attr_name, pattern in kwargs.items():
                 attr_value = variable.attrs.get(attr_name)

xarray/tests/test_dataset.py

@@ -4927,7 +4927,7 @@ def test_filter_by_attrs(self):
                 "temperature_10": (["t"], [0], temp10),
                 "precipitation": (["t"], [0], precip),
             },
-            coords={"time": (["t"], [0], dict(axis="T"))},
+            coords={"time": (["t"], [0], dict(axis="T", long_name="time_in_seconds"))},
         )
 
         # Test return empty Dataset.
@@ -4941,6 +4941,11 @@ def test_filter_by_attrs(self):
 
         assert_equal(new_ds["precipitation"], ds["precipitation"])
 
+        # Test filter coordinates
+        new_ds = ds.filter_by_attrs(long_name="time_in_seconds")
+        assert new_ds["time"].long_name == "time_in_seconds"
+        assert not bool(new_ds.data_vars)
+
         # Test return more than one DataArray.
         new_ds = ds.filter_by_attrs(standard_name="air_potential_temperature")
         assert len(new_ds.data_vars) == 2