Add an axis parameter to DataFrame.diff

Author: evanpw

doc/source/whatsnew/v0.16.1.txt

@@ -16,7 +16,7 @@ We recommend that all users upgrade to this version.
 
 Enhancements
 ~~~~~~~~~~~~
-
+- ``DataFrame.diff`` now takes an ``axis`` parameter
 
 
 

pandas/core/frame.py

@@ -3583,20 +3583,23 @@ def unstack(self, level=-1):
     #----------------------------------------------------------------------
     # Time series-related
 
-    def diff(self, periods=1):
+    def diff(self, periods=1, axis=1):
         """
         1st discrete difference of object
 
         Parameters
         ----------
         periods : int, default 1
             Periods to shift for forming difference
+        axis : {0 or 'index', 1 or 'columns'}
 
         Returns
         -------
         diffed : DataFrame
         """
-        new_data = self._data.diff(n=periods)
+        axis = self._get_axis_number(axis)
+
+        new_data = self._data.diff(n=periods, axis=axis)
         return self._constructor(new_data)
 
     #----------------------------------------------------------------------

pandas/core/internals.py

@@ -868,9 +868,9 @@ def take_nd(self, indexer, axis, new_mgr_locs=None, fill_tuple=None):
     def get_values(self, dtype=None):
         return self.values
 
-    def diff(self, n):
+    def diff(self, n, axis=1):
         """ return block for the diff of the values """
-        new_values = com.diff(self.values, n, axis=1)
+        new_values = com.diff(self.values, n, axis=axis)
         return [make_block(values=new_values,
                            ndim=self.ndim, fastpath=True,
                            placement=self.mgr_locs)]

pandas/tests/test_frame.py

@@ -9955,6 +9955,11 @@ def test_diff_float_n(self):
         xp = self.tsframe.diff(1)
         assert_frame_equal(rs, xp)
 
+    def test_diff_axis(self):
+        df = DataFrame([[1., 2.], [3., 4.]])
+        assert_frame_equal(df.diff(axis=0), DataFrame([[np.nan, 1.], [np.nan, 1.]]))
+        assert_frame_equal(df.diff(axis=1), DataFrame([[np.nan, np.nan], [2., 2.]]))
+
     def test_pct_change(self):
         rs = self.tsframe.pct_change(fill_method=None)
         assert_frame_equal(rs, self.tsframe / self.tsframe.shift(1) - 1)