ENH: level keyword in rename (GH4160)

Author: jorisvandenbossche

doc/source/whatsnew/v0.19.0.txt

@@ -322,6 +322,9 @@ Other enhancements
                        index=['row1', 'row2'])
      df.sort_values(by='row2', axis=1)
 
+- Addition of a ``level`` keyword to ``DataFrame/Series.rename`` to rename
+  labels in the specified level of a MultiIndex (:issue:`4160`).
+
 
 .. _whatsnew_0190.api:
 

pandas/core/generic.py

@@ -588,6 +588,9 @@ def swaplevel(self, i=-2, j=-1, axis=0):
         inplace : boolean, default False
             Whether to return a new %(klass)s. If True then value of copy is
             ignored.
+        level : int or level name, default None
+            In case of a MultiIndex, only rename labels in the specified
+            level.
 
         Returns
         -------
@@ -643,6 +646,7 @@ def rename(self, *args, **kwargs):
         axes, kwargs = self._construct_axes_from_arguments(args, kwargs)
         copy = kwargs.pop('copy', True)
         inplace = kwargs.pop('inplace', False)
+        level = kwargs.pop('level', None)
 
         if kwargs:
             raise TypeError('rename() got an unexpected keyword '
@@ -676,7 +680,10 @@ def f(x):
             f = _get_rename_function(v)
 
             baxis = self._get_block_manager_axis(axis)
-            result._data = result._data.rename_axis(f, axis=baxis, copy=copy)
+            if level is not None:
+                level = self.axes[axis]._get_level_number(level)
+            result._data = result._data.rename_axis(f, axis=baxis, copy=copy,
+                                                    level=level)
             result._clear_item_cache()
 
         if inplace:

pandas/core/internals.py

@@ -2770,7 +2770,7 @@ def set_axis(self, axis, new_labels):
 
         self.axes[axis] = new_labels
 
-    def rename_axis(self, mapper, axis, copy=True):
+    def rename_axis(self, mapper, axis, copy=True, level=None):
         """
         Rename one of axes.
 
@@ -2779,10 +2779,11 @@ def rename_axis(self, mapper, axis, copy=True):
         mapper : unary callable
         axis : int
         copy : boolean, default True
+        level : int, default None
 
         """
         obj = self.copy(deep=copy)
-        obj.set_axis(axis, _transform_index(self.axes[axis], mapper))
+        obj.set_axis(axis, _transform_index(self.axes[axis], mapper, level))
         return obj
 
     def add_prefix(self, prefix):
@@ -4708,15 +4709,20 @@ def _safe_reshape(arr, new_shape):
     return arr
 
 
-def _transform_index(index, func):
+def _transform_index(index, func, level=None):
     """
     Apply function to all values found in index.
 
     This includes transforming multiindex entries separately.
+    Only apply function to one level of the MultiIndex if level is specified.
 
     """
     if isinstance(index, MultiIndex):
-        items = [tuple(func(y) for y in x) for x in index]
+        if level is not None:
+            items = [tuple(func(y) if i == level else y
+                           for i, y in enumerate(x)) for x in index]
+        else:
+            items = [tuple(func(y) for y in x) for x in index]
         return MultiIndex.from_tuples(items, names=index.names)
     else:
         items = [func(x) for x in index]

pandas/tests/frame/test_alter_axes.py

@@ -376,6 +376,64 @@ def test_rename(self):
         self.assertEqual(renamed.index.names, renamer.index.names)
         self.assertEqual(renamed.columns.names, renamer.columns.names)
 
+    def test_rename_multiindex_level(self):
+
+        tuples_index = [('foo1', 'bar1'), ('foo2', 'bar2')]
+        tuples_columns = [('fizz1', 'buzz1'), ('fizz2', 'buzz2')]
+        index = MultiIndex.from_tuples(tuples_index, names=['foo', 'bar'])
+        columns = MultiIndex.from_tuples(
+            tuples_columns, names=['fizz', 'buzz'])
+        renamer = DataFrame([(0, 0), (1, 1)], index=index, columns=columns)
+        renamed = renamer.rename(index={'foo1': 'foo3', 'bar2': 'bar3'},
+                                 columns={'fizz1': 'fizz3', 'buzz2': 'buzz3'})
+
+        # dict
+        new_columns = MultiIndex.from_tuples([('fizz3', 'buzz1'),
+                                              ('fizz2', 'buzz2')],
+                                             names=['fizz', 'buzz'])
+        renamed = renamer.rename(columns={'fizz1': 'fizz3', 'buzz2': 'buzz3'},
+                                 level=0)
+        self.assert_index_equal(renamed.columns, new_columns)
+        renamed = renamer.rename(columns={'fizz1': 'fizz3', 'buzz2': 'buzz3'},
+                                 level='fizz')
+        self.assert_index_equal(renamed.columns, new_columns)
+
+        new_columns = MultiIndex.from_tuples([('fizz1', 'buzz1'),
+                                              ('fizz2', 'buzz3')],
+                                             names=['fizz', 'buzz'])
+        renamed = renamer.rename(columns={'fizz1': 'fizz3', 'buzz2': 'buzz3'},
+                                 level=1)
+        self.assert_index_equal(renamed.columns, new_columns)
+        renamed = renamer.rename(columns={'fizz1': 'fizz3', 'buzz2': 'buzz3'},
+                                 level='buzz')
+        self.assert_index_equal(renamed.columns, new_columns)
+
+        # function
+        func = str.upper
+        new_columns = MultiIndex.from_tuples([('FIZZ1', 'buzz1'),
+                                              ('FIZZ2', 'buzz2')],
+                                             names=['fizz', 'buzz'])
+        renamed = renamer.rename(columns=func, level=0)
+        self.assert_index_equal(renamed.columns, new_columns)
+        renamed = renamer.rename(columns=func, level='fizz')
+        self.assert_index_equal(renamed.columns, new_columns)
+
+        new_columns = MultiIndex.from_tuples([('fizz1', 'BUZZ1'),
+                                              ('fizz2', 'BUZZ2')],
+                                             names=['fizz', 'buzz'])
+        renamed = renamer.rename(columns=func, level=1)
+        self.assert_index_equal(renamed.columns, new_columns)
+        renamed = renamer.rename(columns=func, level='buzz')
+        self.assert_index_equal(renamed.columns, new_columns)
+
+        # index
+        new_index = MultiIndex.from_tuples([('foo3', 'bar1'),
+                                            ('foo2', 'bar2')],
+                                           names=['foo', 'bar'])
+        renamed = renamer.rename(index={'foo1': 'foo3', 'bar2': 'bar3'},
+                                 level=0)
+        self.assert_index_equal(renamed.index, new_index)
+
     def test_rename_nocopy(self):
         renamed = self.frame.rename(columns={'C': 'foo'}, copy=False)
         renamed['foo'] = 1.