From 52b2bd53dc622a6fcdf31a5d577c66063906b0ed Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 9 Oct 2019 12:55:35 -0700
Subject: [PATCH] CLN: dont catch on groupby.mean

---
 pandas/core/groupby/generic.py | 12 ++++++++++++
 pandas/core/groupby/groupby.py | 13 +++----------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 41a5195008f0c..5200d33c6a1fb 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -971,6 +971,18 @@ def _cython_agg_blocks(self, how, alt=None, numeric_only=True, min_count=-1):
                 if result is not no_result:
                     # see if we can cast the block back to the original dtype
                     result = maybe_downcast_numeric(result, block.dtype)
+
+                    if result.ndim == 1 and isinstance(result, np.ndarray):
+                        # e.g. block.values was an IntegerArray
+                        try:
+                            # Cast back if feasible
+                            result = type(block.values)._from_sequence(
+                                result, dtype=block.values.dtype
+                            )
+                        except ValueError:
+                            # reshape to be valid for non-Extension Block
+                            result = result.reshape(1, -1)
+
                     newb = block.make_block(result)
 
             new_items.append(locs)
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 4e0dd65042196..a127e7dc9bada 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -1212,16 +1212,9 @@ def mean(self, *args, **kwargs):
         Name: B, dtype: float64
         """
         nv.validate_groupby_func("mean", args, kwargs, ["numeric_only"])
-        try:
-            return self._cython_agg_general(
-                "mean", alt=lambda x, axis: Series(x).mean(**kwargs), **kwargs
-            )
-        except GroupByError:
-            raise
-        except Exception:
-            with _group_selection_context(self):
-                f = lambda x: x.mean(axis=self.axis, **kwargs)
-                return self._python_agg_general(f)
+        return self._cython_agg_general(
+            "mean", alt=lambda x, axis: Series(x).mean(**kwargs), **kwargs
+        )
 
     @Substitution(name="groupby")
     @Appender(_common_see_also)