bugfix

Author: dcherian

xarray/core/groupby.py

@@ -25,16 +25,14 @@
 
 def check_reduce_dims(reduce_dims, dimensions):
 
-    if is_scalar(reduce_dims):
-        reduce_dims = [reduce_dims]
-
-    if reduce_dims is not ALL_DIMS and any(
-        [dim not in dimensions for dim in reduce_dims]
-    ):
-        raise ValueError(
-            "cannot reduce over dimensions %r. expected either xarray.ALL_DIMS to reduce over all dimensions or one or more of %r."
-            % (reduce_dims, dimensions)
-        )
+    if reduce_dims is not ALL_DIMS:
+        if is_scalar(reduce_dims):
+            reduce_dims = [reduce_dims]
+        if any([dim not in dimensions for dim in reduce_dims]):
+            raise ValueError(
+                "cannot reduce over dimensions %r. expected either xarray.ALL_DIMS to reduce over all dimensions or one or more of %r."
+                % (reduce_dims, dimensions)
+            )
 
 
 def unique_value_groups(ar, sort=True):