Remove workaround for categoricals in stat_summary

The workaround was due to a bug in pandas,
pandas-dev/pandas#10409 that has been fixed.
When that was fixed upstream, the local fix led to another
bug, pandas-dev/pandas#10696!!

Author: has2k1

doc/changelog.rst

@@ -12,6 +12,9 @@ v0.2.1
 - Fixed bug where computed aesthetics could not be used in larger
   statements. (:issue:`7`)
 
+- Fixed bug in :class:`~plotnine.stat_summary` where the you got
+  an exception for some types of the `x` aesthetic values.
+
 
 v0.2.0
 ------

plotnine/stats/stat_summary.py

@@ -204,17 +204,6 @@ def compute_panel(cls, data, scales, **params):
                                 params['fun_ymin'], params['fun_ymax'],
                                 params['fun_args'])
 
-        # NOTE: This is a temporary fix due to bug
-        # https://github.com/pydata/pandas/issues/10409
-        # Remove when that bug is fixed
-        import pandas.api.types as pdtypes
-
-        def preserve_categories(ref, other):
-            for col in ref.columns & other.columns:
-                if pdtypes.is_categorical_dtype(ref[col]):
-                    other[col] = other[col].astype(
-                        'category', categories=ref[col].cat.categories)
-
         # break a dataframe into pieces, summarise each piece,
         # and join the pieces back together, retaining original
         # columns unaffected by the summary.
@@ -227,7 +216,6 @@ def preserve_categories(ref, other):
             if 'y' in unique:
                 unique = unique.drop('y', axis=1)
             merged = summary.merge(unique, on=['group', 'x'])
-            preserve_categories(unique, merged)  # see above note
             summaries.append(merged)
 
         new_data = pd.concat(summaries, axis=0, ignore_index=True)