BUG: df.agg, df.transform and df.apply use different methods when axis=1 than when axis=0 (#21224)

Author: topper-123

Diff for: doc/source/whatsnew/v0.24.0.txt

@@ -475,7 +475,9 @@ Numeric
 - Bug in :class:`Series` ``__rmatmul__`` doesn't support matrix vector multiplication (:issue:`21530`)
 - Bug in :func:`factorize` fails with read-only array (:issue:`12813`)
 - Fixed bug in :func:`unique` handled signed zeros inconsistently: for some inputs 0.0 and -0.0 were treated as equal and for some inputs as different. Now they are treated as equal for all inputs (:issue:`21866`)
--
+- Bug in :meth:`DataFrame.agg`, :meth:`DataFrame.transform` and :meth:`DataFrame.apply` where,
+  when supplied with a list of functions and ``axis=1`` (e.g. ``df.apply(['sum', 'mean'], axis=1)``),
+  a ``TypeError`` was wrongly raised. For all three methods such calculation are now done correctly. (:issue:`16679`).
 -
 
 Strings

Diff for: pandas/conftest.py

@@ -60,6 +60,26 @@ def spmatrix(request):
     return getattr(sparse, request.param + '_matrix')
 
 
+@pytest.fixture(params=[0, 1, 'index', 'columns'],
+                ids=lambda x: "axis {!r}".format(x))
+def axis(request):
+    """
+     Fixture for returning the axis numbers of a DataFrame.
+     """
+    return request.param
+
+
+axis_frame = axis
+
+
+@pytest.fixture(params=[0, 'index'], ids=lambda x: "axis {!r}".format(x))
+def axis_series(request):
+    """
+     Fixture for returning the axis numbers of a Series.
+     """
+    return request.param
+
+
 @pytest.fixture
 def ip():
     """
@@ -103,6 +123,41 @@ def all_arithmetic_operators(request):
     return request.param
 
 
+# use sorted as dicts in py<3.6 have random order, which xdist doesn't like
+_cython_table = sorted(((key, value) for key, value in
+                        pd.core.base.SelectionMixin._cython_table.items()),
+                       key=lambda x: x[0].__class__.__name__)
+
+
+@pytest.fixture(params=_cython_table)
+def cython_table_items(request):
+    return request.param
+
+
+def _get_cython_table_params(ndframe, func_names_and_expected):
+    """combine frame, functions from SelectionMixin._cython_table
+    keys and expected result.
+
+    Parameters
+    ----------
+    ndframe : DataFrame or Series
+    func_names_and_expected : Sequence of two items
+        The first item is a name of a NDFrame method ('sum', 'prod') etc.
+        The second item is the expected return value
+
+    Returns
+    -------
+    results : list
+        List of three items (DataFrame, function, expected result)
+    """
+    results = []
+    for func_name, expected in func_names_and_expected:
+        results.append((ndframe, func_name, expected))
+        results += [(ndframe, func, expected) for func, name in _cython_table
+                    if name == func_name]
+    return results
+
+
 @pytest.fixture(params=['__eq__', '__ne__', '__le__',
                         '__lt__', '__ge__', '__gt__'])
 def all_compare_operators(request):

Diff for: pandas/core/apply.py

@@ -5,6 +5,8 @@
 from pandas.core.dtypes.generic import ABCSeries
 from pandas.core.dtypes.common import (
     is_extension_type,
+    is_dict_like,
+    is_list_like,
     is_sequence)
 from pandas.util._decorators import cache_readonly
 
@@ -105,6 +107,11 @@ def agg_axis(self):
     def get_result(self):
         """ compute the results """
 
+        # dispatch to agg
+        if is_list_like(self.f) or is_dict_like(self.f):
+            return self.obj.aggregate(self.f, axis=self.axis,
+                                      *self.args, **self.kwds)
+
         # all empty
         if len(self.columns) == 0 and len(self.index) == 0:
             return self.apply_empty_result()
@@ -308,15 +315,6 @@ def wrap_results(self):
 class FrameRowApply(FrameApply):
     axis = 0
 
-    def get_result(self):
-
-        # dispatch to agg
-        if isinstance(self.f, (list, dict)):
-            return self.obj.aggregate(self.f, axis=self.axis,
-                                      *self.args, **self.kwds)
-
-        return super(FrameRowApply, self).get_result()
-
     def apply_broadcast(self):
         return super(FrameRowApply, self).apply_broadcast(self.obj)
 

Diff for: pandas/core/frame.py

@@ -6070,19 +6070,34 @@ def _gotitem(self,
     def aggregate(self, func, axis=0, *args, **kwargs):
         axis = self._get_axis_number(axis)
 
-        # TODO: flipped axis
         result = None
-        if axis == 0:
-            try:
-                result, how = self._aggregate(func, axis=0, *args, **kwargs)
-            except TypeError:
-                pass
+        try:
+            result, how = self._aggregate(func, axis=axis, *args, **kwargs)
+        except TypeError:
+            pass
         if result is None:
             return self.apply(func, axis=axis, args=args, **kwargs)
         return result
 
+    def _aggregate(self, arg, axis=0, *args, **kwargs):
+        if axis == 1:
+            # NDFrame.aggregate returns a tuple, and we need to transpose
+            # only result
+            result, how = (super(DataFrame, self.T)
+                           ._aggregate(arg, *args, **kwargs))
+            result = result.T if result is not None else result
+            return result, how
+        return super(DataFrame, self)._aggregate(arg, *args, **kwargs)
+
     agg = aggregate
 
+    @Appender(_shared_docs['transform'] % _shared_doc_kwargs)
+    def transform(self, func, axis=0, *args, **kwargs):
+        axis = self._get_axis_number(axis)
+        if axis == 1:
+            return super(DataFrame, self.T).transform(func, *args, **kwargs).T
+        return super(DataFrame, self).transform(func, *args, **kwargs)
+
     def apply(self, func, axis=0, broadcast=None, raw=False, reduce=None,
               result_type=None, args=(), **kwds):
         """

Diff for: pandas/core/generic.py

@@ -9193,16 +9193,14 @@ def ewm(self, com=None, span=None, halflife=None, alpha=None,
 
         cls.ewm = ewm
 
-        @Appender(_shared_docs['transform'] % _shared_doc_kwargs)
-        def transform(self, func, *args, **kwargs):
-            result = self.agg(func, *args, **kwargs)
-            if is_scalar(result) or len(result) != len(self):
-                raise ValueError("transforms cannot produce "
-                                 "aggregated results")
+    @Appender(_shared_docs['transform'] % _shared_doc_kwargs)
+    def transform(self, func, *args, **kwargs):
+        result = self.agg(func, *args, **kwargs)
+        if is_scalar(result) or len(result) != len(self):
+            raise ValueError("transforms cannot produce "
+                             "aggregated results")
 
-            return result
-
-        cls.transform = transform
+        return result
 
     # ----------------------------------------------------------------------
     # Misc methods