fix resample

Author: jreback

pandas/core/arrays/integer.py

@@ -409,6 +409,11 @@ def nbytes(self):
     def isna(self):
         return self._mask
 
+    @property
+    def flags(self):
+        # compat
+        return self._data.flags
+
     @property
     def _na_value(self):
         return np.nan

pandas/core/groupby/groupby.py

@@ -785,8 +785,12 @@ def _try_cast(self, result, obj, numeric_only=False):
             elif is_extension_array_dtype(dtype):
                 # The function can return something of any type, so check
                 # if the type is compatible with the calling EA.
+
+                # return the same type (Series) as our caller
                 try:
-                    result = obj._values._from_sequence(result, dtype=dtype)
+                    result = result._constructor(
+                        obj._values._from_sequence(result, dtype=dtype),
+                        index=result.index, name=result.name)
                 except Exception:
                     # https://github.com/pandas-dev/pandas/issues/22850
                     # pandas has no control over what 3rd-party ExtensionArrays
@@ -1276,6 +1280,8 @@ def f(self, **kwargs):
                 except Exception:
                     result = self.aggregate(
                         lambda x: npfunc(x, axis=self.axis))
+
+                    result = self._try_cast(result, self.obj)
                     if _convert:
                         result = result._convert(datetime=True)
                     return result

pandas/tests/resample/test_datetime_index.py

@@ -112,6 +112,11 @@ def test_resample_integerarray():
                       dtype="Int64")
     assert_series_equal(result, expected)
 
+    result = ts.resample('3T').mean()
+    expected = Series([1.0, 4, 7],
+                      index=pd.date_range('1/1/2000', periods=3, freq='3T'))
+    assert_series_equal(result, expected)
+
 
 def test_resample_basic_grouper(series):
     s = series