Micro-optimize: Use ._indexes instead of xindexes. (#226)

Author: dcherian

flox/xarray.py

@@ -432,7 +432,7 @@ def wrapper(array, *by, func, skipna, core_dims, **kwargs):
 
     # restore non-dim coord variables without the core dimension
     # TODO: shouldn't apply_ufunc handle this?
-    for var in set(ds_broad.variables) - set(ds_broad.xindexes) - set(ds_broad.dims):
+    for var in set(ds_broad.variables) - set(ds_broad._indexes) - set(ds_broad.dims):
         if all(d not in ds_broad[var].dims for d in dim_tuple):
             actual[var] = ds_broad[var]