More test cases. Clarify whatnew w/ example.

Author: IamJeffG

doc/source/whatsnew/v0.19.0.txt

@@ -229,7 +229,13 @@ Other enhancements
 - ``pd.read_html()`` has gained support for the ``decimal`` option (:issue:`12907`)
 - A top-level function :func:`union_categorical` has been added for combining categoricals, see :ref:`Unioning Categoricals<categorical.union>` (:issue:`13361`)
 - ``Series`` has gained the properties ``.is_monotonic``, ``.is_monotonic_increasing``, ``.is_monotonic_decreasing``, similar to ``Index`` (:issue:`13336`)
-- ``DataFrame.sort_values()`` has gained `axis=1` support to re-order columns with `by=index_label` (:issue:`10806`)
+- ``DataFrame`` has gained support to re-order the columns based on the values in a row using ``df.sort_values(by='index_label', axis=1)`` (:issue:`10806`)
+
+  .. ipython:: python
+
+     df = pd.DataFrame({'A': [2, 7], 'B': [3, 5], 'C': [4, 8]},
+                       index=['row1', 'row2'])
+     df.sort_values(by='row2', axis=1)
 
 .. _whatsnew_0190.api:
 

pandas/tests/frame/test_sorting.py

@@ -125,7 +125,7 @@ def test_sort_values(self):
         expected = frame.reindex(columns=['C', 'B', 'A'])
         assert_frame_equal(sorted_df, expected)
 
-        sorted_df = frame.sort_values(by=[1, 2], axis=1)
+        sorted_df = frame.sort_values(by=[1, 2], axis='columns')
         expected = frame.reindex(columns=['B', 'A', 'C'])
         assert_frame_equal(sorted_df, expected)
 
@@ -150,6 +150,11 @@ def test_sort_values_inplace(self):
         expected = frame.sort_values(by='A')
         assert_frame_equal(sorted_df, expected)
 
+        sorted_df = frame.copy()
+        sorted_df.sort_values(by=1, axis=1, inplace=True)
+        expected = frame.sort_values(by=1, axis=1)
+        assert_frame_equal(sorted_df, expected)
+
         sorted_df = frame.copy()
         sorted_df.sort_values(by='A', ascending=False, inplace=True)
         expected = frame.sort_values(by='A', ascending=False)
@@ -196,6 +201,10 @@ def test_sort_nan(self):
         sorted_df = df.sort_values(['A'], na_position='first', ascending=False)
         assert_frame_equal(sorted_df, expected)
 
+        expected = df.reindex(columns=['B', 'A'])
+        sorted_df = df.sort_values(by=1, axis=1, na_position='first')
+        assert_frame_equal(sorted_df, expected)
+
         # na_position='last', order
         expected = DataFrame(
             {'A': [1, 1, 2, 4, 6, 8, nan],