BUG: fix regression in negative integer indexing from 0.7.x close #1888

Author: wesm

RELEASE.rst

@@ -48,6 +48,8 @@ pandas 0.9.0
   - Add quoting option for DataFrame.to_csv (#1902)
   - Indicate long column value truncation in DataFrame output with ... (#1854)
   - DataFrame.dot will not do data alignment, and also work with Series (#1915)
+  - Add ``na`` option for missing data handling in some vectorized string
+    methods (#1689)
 
 **API Changes**
 
@@ -169,6 +171,11 @@ pandas 0.9.0
   - Raise Exception if set passed to Series constructor (#1913)
   - Add TypeError when appending HDFStore table w/ wrong index type (#1881)
   - Don't raise exception on empty inputs in EW functions (e.g. ewma) (#1900)
+  - Make asof work correctly with PeriodIndex (#1883)
+  - Fix extlinks in doc build
+  - Fill boolean DataFrame with NaN when calling shift (#1814)
+  - Fix setuptools bug causing pip not to Cythonize .pyx files sometimes
+  - Fix negative integer indexing regression in .ix from 0.7.x (#1888)
 
 pandas 0.8.1
 ============

pandas/core/indexing.py

@@ -293,21 +293,27 @@ def _reindex(keys, level=None):
             inds, = np.asarray(key, dtype=bool).nonzero()
             return self.obj.take(inds, axis=axis)
         else:
-            if isinstance(key, Index):
+            was_index = isinstance(key, Index)
+            if was_index:
                 # want Index objects to pass through untouched
                 keyarr = key
             else:
                 # asarray can be unsafe, NumPy strings are weird
                 keyarr = _asarray_tuplesafe(key)
 
             if _is_integer_dtype(keyarr):
+                if labels.inferred_type != 'integer':
+                    keyarr = np.where(keyarr < 0,
+                                      len(labels) + keyarr, keyarr)
+
                 if labels.inferred_type == 'mixed-integer':
                     indexer = labels.get_indexer(keyarr)
                     if (indexer >= 0).all():
                         self.obj.take(indexer, axis=axis)
                     else:
                         return self.obj.take(keyarr, axis=axis)
                 elif not labels.inferred_type == 'integer':
+
                     return self.obj.take(keyarr, axis=axis)
 
             # this is not the most robust, but...
@@ -406,6 +412,9 @@ def _convert_to_indexer(self, obj, axis=0):
 
                 # If have integer labels, defer to label-based indexing
                 if _is_integer_dtype(objarr) and not is_int_index:
+                    if labels.inferred_type != 'integer':
+                        objarr = np.where(objarr < 0,
+                                          len(labels) + objarr, objarr)
                     return objarr
 
                 # this is not the most robust, but...

pandas/tests/test_frame.py

@@ -175,6 +175,22 @@ def test_getitem_ix_mixed_integer(self):
         expected = df.ix[Index([1, 10], dtype=object)]
         assert_frame_equal(result, expected)
 
+    def test_getitem_setitem_ix_negative_integers(self):
+        result = self.frame.ix[:, -1]
+        assert_series_equal(result, self.frame['D'])
+
+        result = self.frame.ix[:, [-1]]
+        assert_frame_equal(result, self.frame[['D']])
+
+        result = self.frame.ix[:, [-1, -2]]
+        assert_frame_equal(result, self.frame[['D', 'C']])
+
+        self.frame.ix[:, [-1]] = 0
+        self.assert_((self.frame['D'] == 0).all())
+
+        df = DataFrame(np.random.randn(8, 4))
+        self.assert_(isnull(df.ix[:, [-1]].values).all())
+
     def test_getattr(self):
         tm.assert_series_equal(self.frame.A, self.frame['A'])
         self.assertRaises(AttributeError, getattr, self.frame,