correct apply(axis=1) and related bugs

Author: tp

doc/source/whatsnew/v0.24.0.txt

@@ -405,7 +405,11 @@ 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`)
--
+- Bug in :meth:`DataFrame.agg`, :meth:`DataFrame.transform` and :meth:`DataFrame.apply` when ``axis=1``.
+  Using ``apply`` with a list on functions and axis=1 (e.g. ``df.apply(['abs'], axis=1)``)
+  previously gave an TypeError, while the operation worked with axis=0. This fixes that issue.
+  As ``agg`` and ``transform`` in many cases delegated to ``apply``, this also
+  fixed this issue for them also (:issue:`16679`).
 -
 
 Strings

pandas/core/apply.py

@@ -105,6 +105,11 @@ def agg_axis(self):
     def get_result(self):
         """ compute the results """
 
+        # dispatch to agg
+        if isinstance(self.f, (list, dict)):
+            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 +313,6 @@ 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)
 

pandas/core/frame.py

@@ -6077,11 +6077,20 @@ def aggregate(self, func, axis=0, *args, **kwargs):
         return result
 
     def _aggregate(self, arg, axis=0, *args, **kwargs):
-        obj = self.T if axis == 1 else self
-        return super(DataFrame, obj)._aggregate(arg, *args, **kwargs)
+        if axis == 1:
+            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
 
+    def transform(self, func, axis=0, *args, **kwargs):
+        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):
         """

pandas/core/generic.py

@@ -9090,16 +9090,14 @@ 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

pandas/tests/frame/test_apply.py

@@ -846,58 +846,74 @@ def test_consistency_for_boxed(self, box):
         assert_frame_equal(result, expected)
 
 
-def zip_frames(*frames):
+def zip_frames(*frames, axis=1):
     """
-    take a list of frames, zip the columns together for each
-    assume that these all have the first frame columns
+    take a list of frames, zip them together under the
+    assumption that these all have the first frames' index/columns.
 
-    return a new frame
+    Returns
+    -------
+    new_frame : DataFrame
     """
-    columns = frames[0].columns
-    zipped = [f[c] for c in columns for f in frames]
-    return pd.concat(zipped, axis=1)
+    if axis == 1:
+        columns = frames[0].columns
+        zipped = [f.loc[:, c] for c in columns for f in frames]
+        return pd.concat(zipped, axis=1)
+    else:
+        index = frames[0].index
+        zipped = [f.loc[i, :] for i in index for f in frames]
+        return pd.DataFrame(zipped)
 
 
 class TestDataFrameAggregate(TestData):
 
-    def test_agg_transform(self):
+    def test_agg_transform(self, axis):
+        other_axis = abs(axis - 1)
 
         with np.errstate(all='ignore'):
 
-            f_sqrt = np.sqrt(self.frame)
             f_abs = np.abs(self.frame)
+            f_sqrt = np.sqrt(self.frame)
 
             # ufunc
-            result = self.frame.transform(np.sqrt)
+            result = self.frame.transform(np.sqrt, axis=axis)
             expected = f_sqrt.copy()
             assert_frame_equal(result, expected)
 
-            result = self.frame.apply(np.sqrt)
+            result = self.frame.apply(np.sqrt, axis=axis)
             assert_frame_equal(result, expected)
 
-            result = self.frame.transform(np.sqrt)
+            result = self.frame.transform(np.sqrt, axis=axis)
             assert_frame_equal(result, expected)
 
             # list-like
-            result = self.frame.apply([np.sqrt])
+            result = self.frame.apply([np.sqrt], axis=axis)
             expected = f_sqrt.copy()
-            expected.columns = pd.MultiIndex.from_product(
-                [self.frame.columns, ['sqrt']])
+            if axis == 0:
+                expected.columns = pd.MultiIndex.from_product(
+                    [self.frame.columns, ['sqrt']])
+            else:
+                expected.index = pd.MultiIndex.from_product(
+                    [self.frame.index, ['sqrt']])
             assert_frame_equal(result, expected)
 
-            result = self.frame.transform([np.sqrt])
+            result = self.frame.transform([np.sqrt], axis=axis)
             assert_frame_equal(result, expected)
 
             # multiple items in list
             # these are in the order as if we are applying both
             # functions per series and then concatting
-            expected = zip_frames(f_sqrt, f_abs)
-            expected.columns = pd.MultiIndex.from_product(
-                [self.frame.columns, ['sqrt', 'absolute']])
-            result = self.frame.apply([np.sqrt, np.abs])
+            result = self.frame.apply([np.abs, np.sqrt], axis=axis)
+            expected = zip_frames(f_abs, f_sqrt, axis=other_axis)
+            if axis == 0:
+                expected.columns = pd.MultiIndex.from_product(
+                    [self.frame.columns, ['absolute', 'sqrt']])
+            else:
+                expected.index = pd.MultiIndex.from_product(
+                    [self.frame.index, ['absolute', 'sqrt']])
             assert_frame_equal(result, expected)
 
-            result = self.frame.transform(['sqrt', np.abs])
+            result = self.frame.transform([np.abs, 'sqrt'], axis=axis)
             assert_frame_equal(result, expected)
 
     def test_transform_and_agg_err(self, axis):
@@ -985,13 +1001,16 @@ def test_agg_dict_nested_renaming_depr(self):
 
     def test_agg_reduce(self, axis):
         other_axis = abs(axis - 1)
-        name1, name2 = self.frame.axes[other_axis].unique()[:2]
+        name1, name2 = self.frame.axes[other_axis].unique()[:2].sort_values()
 
         # all reducers
-        expected = zip_frames(self.frame.mean(axis=axis).to_frame(),
-                              self.frame.max(axis=axis).to_frame(),
-                              self.frame.sum(axis=axis).to_frame()).T
-        expected.index = ['mean', 'max', 'sum']
+        expected = pd.concat([self.frame.mean(axis=axis),
+                              self.frame.max(axis=axis),
+                              self.frame.sum(axis=axis),
+                              ], axis=1)
+        expected.columns = ['mean', 'max', 'sum']
+        expected = expected.T if axis == 0 else expected
+
         result = self.frame.agg(['mean', 'max', 'sum'], axis=axis)
         assert_frame_equal(result, expected)
 
@@ -1001,7 +1020,7 @@ def test_agg_reduce(self, axis):
         expected = Series([self.frame.loc(other_axis)[name1].mean(),
                            self.frame.loc(other_axis)[name2].sum()],
                           index=[name1, name2])
-        assert_series_equal(result.reindex_like(expected), expected)
+        assert_series_equal(result, expected)
 
         # dict input with lists
         func = {name1: ['mean'], name2: ['sum']}
@@ -1011,7 +1030,8 @@ def test_agg_reduce(self, axis):
                           index=['mean']),
             name2: Series([self.frame.loc(other_axis)[name2].sum()],
                           index=['sum'])})
-        assert_frame_equal(result.reindex_like(expected), expected)
+        expected = expected.T if axis == 1 else expected
+        assert_frame_equal(result, expected)
 
         # dict input with lists with multiple
         func = {name1: ['mean', 'sum'],
@@ -1024,7 +1044,8 @@ def test_agg_reduce(self, axis):
             name2: Series([self.frame.loc(other_axis)[name2].sum(),
                            self.frame.loc(other_axis)[name2].max()],
                           index=['sum', 'max'])})
-        assert_frame_equal(result.reindex_like(expected), expected)
+        expected = expected.T if axis == 1 else expected
+        assert_frame_equal(result, expected)
 
     def test_nuiscance_columns(self):