Propagate attrs better (#124)

Author: dcherian

flox/xarray.py

@@ -366,7 +366,7 @@ def wrapper(array, *by, func, skipna, **kwargs):
         if all(d not in ds[var].dims for d in dim):
             actual[var] = ds[var]
 
-    for name, expect in zip(group_names, expected_groups):
+    for name, expect, by_ in zip(group_names, expected_groups, by):
         # Can't remove this till xarray handles IntervalIndex
         if isinstance(expect, pd.IntervalIndex):
             expect = expect.to_numpy()
@@ -382,6 +382,8 @@ def wrapper(array, *by, func, skipna, **kwargs):
                 actual = actual.set_coords(levelnames)
         else:
             actual[name] = expect
+        if keep_attrs:
+            actual[name].attrs = by_.attrs
 
     if unindexed_dims:
         actual = actual.drop_vars(unindexed_dims)