ENH: Implement Panel pct_change

doc/source/computation.rst

@@ -26,9 +26,9 @@ Statistical functions
 Percent Change
 ~~~~~~~~~~~~~~
 
-Both ``Series`` and ``DataFrame`` has a method ``pct_change`` to compute the
+``Series``, ``DataFrame``, and ``Panel`` all have a method ``pct_change`` to compute the
 percent change over a given number of periods (using ``fill_method`` to fill
-NA/null values).
+NA/null values *before* computing the percent change).
 
 .. ipython:: python
 

doc/source/release.rst

@@ -63,7 +63,7 @@ New features
   noon, January 1, 4713 BC.  Because nanoseconds are used to define the time
   in pandas the actual range of dates that you can use is 1678 AD to 2262 AD. (:issue:`4041`)
 - Added error bar support to the ``.plot`` method of ``DataFrame`` and ``Series`` (:issue:`3796`)
-
+- Implemented ``Panel.pct_change`` (:issue:`6904`)
 
 API Changes
 ~~~~~~~~~~~

doc/source/v0.14.0.txt

@@ -470,6 +470,7 @@ Enhancements
 - :ref:`Holidays Calendars<timeseries.holiday>` are now available and can be used with CustomBusinessDay (:issue:`6719`)
 - ``Float64Index`` is now backed by a ``float64`` dtype ndarray instead of an
   ``object`` dtype array (:issue:`6471`).
+- Implemented ``Panel.pct_change`` (:issue:`6904`)
 
 Performance
 ~~~~~~~~~~~

pandas/core/generic.py

@@ -3455,10 +3455,8 @@ def _convert_timedeltas(x):
 
         return np.abs(self)
 
-    def pct_change(self, periods=1, fill_method='pad', limit=None, freq=None,
-                   **kwds):
-        """
-        Percent change over given number of periods
+    _shared_docs['pct_change'] = """
+        Percent change over given number of periods.
 
         Parameters
         ----------
@@ -3473,14 +3471,27 @@ def pct_change(self, periods=1, fill_method='pad', limit=None, freq=None,
 
         Returns
         -------
-        chg : same type as caller
+        chg : %(klass)s
+
+        Notes
+        -----
+
+        By default, the percentage change is calculated along the stat
+        axis: 0, or ``Index``, for ``DataFrame`` and 1, or ``minor`` for
+        ``Panel``. You can change this with the ``axis`` keyword argument.
         """
+
+    @Appender(_shared_docs['pct_change'] % _shared_doc_kwargs)
+    def pct_change(self, periods=1, fill_method='pad', limit=None, freq=None,
+                   **kwds):
         # TODO: Not sure if above is correct - need someone to confirm.
+        axis = self._get_axis_number(kwds.pop('axis', self._stat_axis_name))
         if fill_method is None:
             data = self
         else:
             data = self.fillna(method=fill_method, limit=limit)
-        rs = data / data.shift(periods=periods, freq=freq, **kwds) - 1
+
+        rs = data.div(data.shift(periods, freq=freq, axis=axis, **kwds)) - 1
         if freq is None:
             mask = com.isnull(_values_from_object(self))
             np.putmask(rs.values, mask, np.nan)

pandas/core/panel.py

@@ -1116,7 +1116,7 @@ def count(self, axis='major'):
 
     def shift(self, lags, freq=None, axis='major'):
         """
-        Shift major or minor axis by specified number of leads/lags. 
+        Shift major or minor axis by specified number of leads/lags.
 
         Parameters
         ----------

pandas/tests/test_panel.py

@@ -1684,6 +1684,60 @@ def test_tshift(self):
         no_freq = panel.ix[:, [0, 5, 7], :]
         self.assertRaises(ValueError, no_freq.tshift)
 
+    def test_pct_change(self):
+        df1 = DataFrame({'c1': [1, 2, 5], 'c2': [3, 4, 6]})
+        df2 = df1 + 1
+        df3 = DataFrame({'c1': [3, 4, 7], 'c2': [5, 6, 8]})
+        wp = Panel({'i1': df1, 'i2': df2, 'i3': df3})
+        # major, 1
+        result = wp.pct_change()  # axis='major'
+        expected = Panel({'i1': df1.pct_change(),
+                          'i2': df2.pct_change(),
+                          'i3': df3.pct_change()})
+        assert_panel_equal(result, expected)
+        result = wp.pct_change(axis=1)
+        assert_panel_equal(result, expected)
+        # major, 2
+        result = wp.pct_change(periods=2)
+        expected = Panel({'i1': df1.pct_change(2),
+                          'i2': df2.pct_change(2),
+                          'i3': df3.pct_change(2)})
+        assert_panel_equal(result, expected)
+        # minor, 1
+        result = wp.pct_change(axis='minor')
+        expected = Panel({'i1': df1.pct_change(axis=1),
+                          'i2': df2.pct_change(axis=1),
+                          'i3': df3.pct_change(axis=1)})
+        assert_panel_equal(result, expected)
+        result = wp.pct_change(axis=2)
+        assert_panel_equal(result, expected)
+        # minor, 2
+        result = wp.pct_change(periods=2, axis='minor')
+        expected = Panel({'i1': df1.pct_change(periods=2, axis=1),
+                          'i2': df2.pct_change(periods=2, axis=1),
+                          'i3': df3.pct_change(periods=2, axis=1)})
+        assert_panel_equal(result, expected)
+        # items, 1
+        result = wp.pct_change(axis='items')
+        expected = Panel({'i1': DataFrame({'c1': [np.nan, np.nan, np.nan],
+                                           'c2': [np.nan, np.nan, np.nan]}),
+                          'i2': DataFrame({'c1': [1, 0.5, .2],
+                                           'c2': [1./3, 0.25, 1./6]}),
+                          'i3': DataFrame({'c1': [.5, 1./3, 1./6],
+                                           'c2': [.25, .2, 1./7]})})
+        assert_panel_equal(result, expected)
+        result = wp.pct_change(axis=0)
+        assert_panel_equal(result, expected)
+        # items, 2
+        result = wp.pct_change(periods=2, axis='items')
+        expected = Panel({'i1': DataFrame({'c1': [np.nan, np.nan, np.nan],
+                                           'c2': [np.nan, np.nan, np.nan]}),
+                          'i2': DataFrame({'c1': [np.nan, np.nan, np.nan],
+                                           'c2': [np.nan, np.nan, np.nan]}),
+                          'i3': DataFrame({'c1': [2, 1, .4],
+                                           'c2': [2./3, .5, 1./3]})})
+        assert_panel_equal(result, expected)
+
     def test_multiindex_get(self):
         ind = MultiIndex.from_tuples([('a', 1), ('a', 2), ('b', 1), ('b', 2)],
                                      names=['first', 'second'])

vb_suite/panel_methods.py

@@ -17,3 +17,12 @@
 
 panel_shift_minor = Benchmark('panel.shift(1, axis=minor)', setup,
                                start_date=datetime(2012, 1, 12))
+
+panel_pct_change_major = Benchmark('panel.pct_change(1, axis="major")', setup,
+                                   start_date=datetime(2014, 4, 19))
+
+panel_pct_change_minor = Benchmark('panel.pct_change(1, axis="minor")', setup,
+                                   start_date=datetime(2014, 4, 19))
+
+panel_pct_change_items = Benchmark('panel.pct_change(1, axis="items")', setup,
+                                   start_date=datetime(2014, 4, 19))