Merge branch 'master' of https://github.com/pandas-dev/pandas into re…

…f-blockwise-3

pandas/core/groupby/generic.py

@@ -1094,25 +1094,20 @@ def blk_func(block: "Block") -> List["Block"]:
                 sgb = get_groupby(obj, self.grouper, observed=True)
                 result = sgb.aggregate(lambda x: alt(x, axis=self.axis))
 
-                result = cast(DataFrame, result)
+                assert isinstance(result, (Series, DataFrame))  # for mypy
+                # In the case of object dtype block, it may have been split
+                #  in the operation.  We un-split here.
+                result = result._consolidate()
+                assert isinstance(result, (Series, DataFrame))  # for mypy
+                assert len(result._mgr.blocks) == 1
+
                 # unwrap DataFrame to get array
-                if len(result._mgr.blocks) != 1:
-                    # We've split an object block! Everything we've assumed
-                    # about a single block input returning a single block output
-                    # is a lie. To keep the code-path for the typical non-split case
-                    # clean, we choose to clean up this mess later on.
-                    assert len(locs) == result.shape[1]
-                    for i, loc in enumerate(locs):
-                        agg_block = result.iloc[:, [i]]._mgr.blocks[0]
-                        agg_block.mgr_locs = [loc]
-                        new_blocks.append(agg_block)
-                else:
-                    result = result._mgr.blocks[0].values
-                    if isinstance(result, np.ndarray) and result.ndim == 1:
-                        result = result.reshape(1, -1)
-                    res_values = cast_agg_result(result, block.values, how)
-                    agg_block = block.make_block(res_values)
-                    new_blocks = [agg_block]
+                result = result._mgr.blocks[0].values
+                if isinstance(result, np.ndarray) and result.ndim == 1:
+                    result = result.reshape(1, -1)
+                res_values = cast_agg_result(result, block.values, how)
+                agg_block = block.make_block(res_values)
+                new_blocks = [agg_block]
             else:
                 res_values = cast_agg_result(result, block.values, how)
                 agg_block = block.make_block(res_values)