BUG: cache coherence issue with chain indexing and setitem (GH7084)

doc/source/release.rst

@@ -482,6 +482,8 @@ Bug Fixes
   were being passed to plotting method
 - :func:`read_fwf` treats ``None`` in ``colspec`` like regular python slices. It now reads from the beginning
   or until the end of the line when ``colspec`` contains a ``None`` (previously raised a ``TypeError``)
+- Bug in cache coherence with chained indexing and slicing; add ``_is_view`` property to ``NDFrame`` to correctly predict
+  views; mark ``is_copy`` on ``xs` only if its an actual copy (and not a view) (:issue:`7084`)
 
 pandas 0.13.1
 -------------

pandas/core/frame.py

@@ -1632,7 +1632,7 @@ def _ixs(self, i, axis=0):
                     name=label, fastpath=True)
 
                 # this is a cached value, mark it so
-                result._set_as_cached(i, self)
+                result._set_as_cached(label, self)
 
                 return result
 

pandas/core/generic.py

@@ -1091,6 +1091,11 @@ def _is_cached(self):
         cacher = getattr(self, '_cacher', None)
         return cacher is not None
 
+    @property
+    def _is_view(self):
+        """ boolean : return if I am a view of another array """
+        return self._data.is_view
+
     def _maybe_update_cacher(self, clear=False):
         """ see if we need to update our parent cacher
             if clear, then clear our cache """
@@ -1372,7 +1377,9 @@ def xs(self, key, axis=0, level=None, copy=None, drop_level=True):
             result = self[loc]
             result.index = new_index
 
-        result._set_is_copy(self)
+        # this could be a view
+        # but only in a single-dtyped view slicable case
+        result._set_is_copy(self, copy=not result._is_view)
         return result
 
     _xs = xs

pandas/core/internals.py

@@ -2289,6 +2289,13 @@ def is_datelike_mixed_type(self):
         self._consolidate_inplace()
         return any([block.is_datelike for block in self.blocks])
 
+    @property
+    def is_view(self):
+        """ return a boolean if we are a single block and are a view """
+        if len(self.blocks) == 1:
+            return self.blocks[0].values.base is not None
+        return False
+
     def get_bool_data(self, copy=False):
         """
         Parameters

pandas/core/series.py

@@ -693,6 +693,7 @@ def _set_values(self, key, value):
         if isinstance(key, Series):
             key = key.values
         self._data = self._data.setitem(indexer=key, value=value)
+        self._maybe_update_cacher()
 
     # help out SparseSeries
     _get_val_at = ndarray.__getitem__

pandas/tests/test_indexing.py

@@ -2666,9 +2666,10 @@ def test_cache_updating(self):
         df.index = index
 
         # setting via chained assignment
-        def f():
-            df.loc[0]['z'].iloc[0] = 1.
-        self.assertRaises(com.SettingWithCopyError, f)
+        # but actually works, since everything is a view
+        df.loc[0]['z'].iloc[0] = 1.
+        result = df.loc[(0,0),'z']
+        self.assertEqual(result, 1)
 
         # correct setting
         df.loc[(0,0),'z'] = 2
@@ -2710,6 +2711,28 @@ def test_setitem_cache_updating(self):
             self.assertEqual(df.ix[0,'c'], 0.0)
             self.assertEqual(df.ix[7,'c'], 1.0)
 
+        # GH 7084
+        # not updating cache on series setting with slices
+        out = DataFrame({'A': [0, 0, 0]}, index=date_range('5/7/2014', '5/9/2014'))
+        df = DataFrame({'C': ['A', 'A', 'A'], 'D': [100, 200, 300]})
+
+        #loop through df to update out
+        six = Timestamp('5/7/2014')
+        eix = Timestamp('5/9/2014')
+        for ix, row in df.iterrows():
+            out[row['C']][six:eix] = out[row['C']][six:eix] + row['D']
+
+        expected = DataFrame({'A': [600, 600, 600]}, index=date_range('5/7/2014', '5/9/2014'))
+        assert_frame_equal(out, expected)
+        assert_series_equal(out['A'], expected['A'])
+
+        out = DataFrame({'A': [0, 0, 0]}, index=date_range('5/7/2014', '5/9/2014'))
+        for ix, row in df.iterrows():
+            out.loc[six:eix,row['C']] += row['D']
+
+        assert_frame_equal(out, expected)
+        assert_series_equal(out['A'], expected['A'])
+
     def test_setitem_chained_setfault(self):
 
         # GH6026