Merge pull request #3125 from jreback/GH2903

BUG: GH2903 implemented xs for axis=1 with a level specified

Author: jreback

RELEASE.rst

@@ -219,8 +219,9 @@ pandas 0.11.0
   - Fix NameError issue on RESO_US (GH2787_)
   - Allow selection in an *unordered* timeseries to work similary 
     to an *ordered* timeseries (GH2437_).
+  - Fix implemented ``.xs`` when called with ``axes=1`` and a level parameter (GH2903_)
 
- .. _GH2758: https://github.com/pydata/pandas/issues/2758
+.. _GH2758: https://github.com/pydata/pandas/issues/2758
 .. _GH2809: https://github.com/pydata/pandas/issues/2809
 .. _GH2810: https://github.com/pydata/pandas/issues/2810
 .. _GH2837: https://github.com/pydata/pandas/issues/2837
@@ -257,6 +258,7 @@ pandas 0.11.0
 .. _GH2850: https://github.com/pydata/pandas/issues/2850
 .. _GH2898: https://github.com/pydata/pandas/issues/2898
 .. _GH2892: https://github.com/pydata/pandas/issues/2892
+.. _GH2903: https://github.com/pydata/pandas/issues/2903
 .. _GH2909: https://github.com/pydata/pandas/issues/2909
 .. _GH2922: https://github.com/pydata/pandas/issues/2922
 .. _GH2929: https://github.com/pydata/pandas/issues/2929

pandas/core/frame.py

@@ -2211,7 +2211,11 @@ def xs(self, key, axis=0, level=None, copy=True):
                 if labels.levels[lev_num].inferred_type == 'integer':
                     indexer = self.index[loc]
 
-            result = self.ix[indexer]
+            # select on the correct axis
+            if axis == 1:
+                result = self.ix[:, indexer]
+            else:
+                result = self.ix[indexer]
             setattr(result, result._get_axis_name(axis), new_ax)
             return result
 

pandas/tests/test_indexing.py

@@ -714,6 +714,16 @@ def test_ix_general(self):
         df.sortlevel(inplace=True)
         df.ix[(4.0,2012)]
 
+    def test_xs_multiindex(self):
+
+        # GH2903
+        columns = MultiIndex.from_tuples([('a', 'foo'), ('a', 'bar'), ('b', 'hello'), ('b', 'world')], names=['lvl0', 'lvl1'])
+        df = DataFrame(np.random.randn(4, 4), columns=columns)
+        df.sortlevel(axis=1,inplace=True)
+        result = df.xs('a', level='lvl0', axis=1)
+        expected = df.iloc[:,0:2].loc[:,'a']
+        assert_frame_equal(result,expected)
+
 if __name__ == '__main__':
     import nose
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],