PERF: speed up concat on Series by skipping unnecessary DataFrame creation

doc/source/whatsnew/v0.24.0.txt

@@ -1060,6 +1060,7 @@ Performance Improvements
 - Improved the performance of :func:`pandas.get_dummies` with ``sparse=True`` (:issue:`21997`)
 - Improved performance of :func:`IndexEngine.get_indexer_non_unique` for sorted, non-unique indexes (:issue:`9466`)
 - Improved performance of :func:`PeriodIndex.unique` (:issue:`23083`)
+- Improved performance of :func:`pd.concat` for `Series` objects (:issue:`23404`)
 
 
 .. _whatsnew_0240.docs:

pandas/core/generic.py

@@ -358,41 +358,44 @@ def _from_axes(cls, data, axes, **kwargs):
             d.update(kwargs)
             return cls(data, **d)
 
-    def _get_axis_number(self, axis):
-        axis = self._AXIS_ALIASES.get(axis, axis)
+    @classmethod
+    def _get_axis_number(cls, axis):
+        axis = cls._AXIS_ALIASES.get(axis, axis)
         if is_integer(axis):
-            if axis in self._AXIS_NAMES:
+            if axis in cls._AXIS_NAMES:
                 return axis
         else:
             try:
-                return self._AXIS_NUMBERS[axis]
+                return cls._AXIS_NUMBERS[axis]
             except KeyError:
                 pass
         raise ValueError('No axis named {0} for object type {1}'
-                         .format(axis, type(self)))
+                         .format(axis, type(cls)))
 
-    def _get_axis_name(self, axis):
-        axis = self._AXIS_ALIASES.get(axis, axis)
+    @classmethod
+    def _get_axis_name(cls, axis):
+        axis = cls._AXIS_ALIASES.get(axis, axis)
         if isinstance(axis, string_types):
-            if axis in self._AXIS_NUMBERS:
+            if axis in cls._AXIS_NUMBERS:
                 return axis
         else:
             try:
-                return self._AXIS_NAMES[axis]
+                return cls._AXIS_NAMES[axis]
             except KeyError:
                 pass
         raise ValueError('No axis named {0} for object type {1}'
-                         .format(axis, type(self)))
+                         .format(axis, type(cls)))
 
     def _get_axis(self, axis):
         name = self._get_axis_name(axis)
         return getattr(self, name)
 
-    def _get_block_manager_axis(self, axis):
+    @classmethod
+    def _get_block_manager_axis(cls, axis):
         """Map the axis to the block_manager axis."""
-        axis = self._get_axis_number(axis)
-        if self._AXIS_REVERSED:
-            m = self._AXIS_LEN - 1
+        axis = cls._get_axis_number(axis)
+        if cls._AXIS_REVERSED:
+            m = cls._AXIS_LEN - 1
             return m - axis
         return axis
 

pandas/core/reshape/concat.py

@@ -322,7 +322,7 @@ def __init__(self, objs, axis=0, join='outer', join_axes=None,
 
         # Standardize axis parameter to int
         if isinstance(sample, Series):
-            axis = DataFrame()._get_axis_number(axis)
+            axis = DataFrame._get_axis_number(axis)
         else:
             axis = sample._get_axis_number(axis)
 

pandas/tests/generic/test_generic.py

@@ -1019,3 +1019,15 @@ def test_pipe_panel(self):
 
             with pytest.raises(ValueError):
                 result = wp.pipe((f, 'y'), x=1, y=1)
+
+    @pytest.mark.parametrize('box', [pd.Series, pd.DataFrame])
+    def test_axis_classmethods(self, box):
+        obj = box()
+        values = (list(box._AXIS_NAMES.keys()) +
+                  list(box._AXIS_NUMBERS.keys()) +
+                  list(box._AXIS_ALIASES.keys()))
+        for v in values:
+            assert obj._get_axis_number(v) == box._get_axis_number(v)
+            assert obj._get_axis_name(v) == box._get_axis_name(v)
+            assert obj._get_block_manager_axis(v) == \
+                box._get_block_manager_axis(v)