From 1b23b6fda648ec864ecc7865b385ba525f5d6182 Mon Sep 17 00:00:00 2001
From: Wes McKinney <wesmckinn@gmail.com>
Date: Fri, 2 Nov 2012 20:22:39 -0400
Subject: [PATCH] BUG: make NDFrame.drop work with non-unique indexes. close
 #2101

---
 pandas/core/generic.py          | 24 +++++++++++++++++++-----
 pandas/tests/test_frame.py      | 15 ---------------
 pandas/tests/test_multilevel.py | 21 +++++++++++++++++++++
 3 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 31c1c2a638376..cf2557d84e8fe 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -7,6 +7,7 @@
 from pandas.tseries.index import DatetimeIndex
 from pandas.tseries.offsets import DateOffset
 import pandas.core.common as com
+import pandas.lib as lib
 
 
 class PandasError(Exception):
@@ -337,13 +338,26 @@ def drop(self, labels, axis=0, level=None):
         axis_name = self._get_axis_name(axis)
         axis = self._get_axis(axis)
 
-        if level is not None:
-            assert(isinstance(axis, MultiIndex))
-            new_axis = axis.drop(labels, level=level)
+        if axis.is_unique:
+            if level is not None:
+                assert(isinstance(axis, MultiIndex))
+                new_axis = axis.drop(labels, level=level)
+            else:
+                new_axis = axis.drop(labels)
+
+            return self.reindex(**{axis_name: new_axis})
         else:
-            new_axis = axis.drop(labels)
+            if level is not None:
+                assert(isinstance(axis, MultiIndex))
+                indexer = -lib.ismember(axis.get_level_values(level),
+                                        set(labels))
+            else:
+                indexer = -axis.isin(labels)
 
-        return self.reindex(**{axis_name: new_axis})
+            slicer = [slice(None)] * self.ndim
+            slicer[self._get_axis_number(axis_name)] = indexer
+
+            return self.ix[tuple(slicer)]
 
     def sort_index(self, axis=0, ascending=True):
         """
diff --git a/pandas/tests/test_frame.py b/pandas/tests/test_frame.py
index 2282ea6ad7b4d..f069a65a1ab12 100644
--- a/pandas/tests/test_frame.py
+++ b/pandas/tests/test_frame.py
@@ -4366,21 +4366,6 @@ def test_drop_col_still_multiindex(self):
         del df[('a','','')]
         assert(isinstance(df.columns, MultiIndex))
 
-    def test_drop_nonuq_multiindex(self):
-        df = DataFrame([["x-a", "x", "a", 1.5],["x-a", "x", "a", 1.2],
-                        ["z-c", "z", "c", 3.1], ["x-a", "x", "a", 4.1],
-                        ["x-b", "x", "b", 5.1],["x-b", "x", "b", 4.1],
-                        ["x-b", "x", "b", 2.2],
-                        ["y-a", "y", "a", 1.2],["z-b", "z", "b", 2.1]],
-                       columns=["var1", "var2", "var3", "var4"])
-
-        grp_size = df.groupby("var1").size()
-        drop_idx = grp_size.ix[grp_size == 1]
-
-        df = df.set_index(["var1", "var2", "var3"])
-
-        self.assertRaises(Exception, df.drop, drop_idx.index, level=0)
-
     def test_fillna(self):
         self.tsframe['A'][:5] = nan
         self.tsframe['A'][-5:] = nan
diff --git a/pandas/tests/test_multilevel.py b/pandas/tests/test_multilevel.py
index 34872ea572f81..900ba1137cd9e 100644
--- a/pandas/tests/test_multilevel.py
+++ b/pandas/tests/test_multilevel.py
@@ -1326,6 +1326,27 @@ def test_mixed_depth_drop(self):
                             ('routine2', 'result1', '')], axis=1)
         assert_frame_equal(expected, result)
 
+    def test_drop_nonunique(self):
+        df = DataFrame([["x-a", "x", "a", 1.5],["x-a", "x", "a", 1.2],
+                        ["z-c", "z", "c", 3.1], ["x-a", "x", "a", 4.1],
+                        ["x-b", "x", "b", 5.1],["x-b", "x", "b", 4.1],
+                        ["x-b", "x", "b", 2.2],
+                        ["y-a", "y", "a", 1.2],["z-b", "z", "b", 2.1]],
+                       columns=["var1", "var2", "var3", "var4"])
+
+        grp_size = df.groupby("var1").size()
+        drop_idx = grp_size.ix[grp_size == 1]
+
+        idf = df.set_index(["var1", "var2", "var3"])
+
+        # it works! #2101
+        result = idf.drop(drop_idx.index, level=0).reset_index()
+        expected = df[-df.var1.isin(drop_idx.index)]
+
+        result.index = expected.index
+
+        assert_frame_equal(result, expected)
+
     def test_mixed_depth_pop(self):
         arrays = [[  'a', 'top', 'top', 'routine1', 'routine1', 'routine2'],
                   [   '',  'OD',  'OD', 'result1',   'result2',  'result1'],