BUG: Mismatch between get and set behavior for slices of floating indices

Author: stephenwlin

pandas/core/indexing.py

@@ -435,23 +435,27 @@ def _convert_to_indexer(self, obj, axis=0):
         if isinstance(obj, slice):
             ltype = labels.inferred_type
 
-            if ltype == 'floating':
-                int_slice = _is_int_slice(obj)
-            else:
-                # floats that are within tolerance of int used
-                int_slice = _is_index_slice(obj)
+            # in case of providing all floats, use label-based indexing
+            float_slice = (labels.inferred_type == 'floating'
+                           and _is_float_slice(obj))
+
+            # floats that are within tolerance of int used as positions
+            int_slice = _is_index_slice(obj)
 
             null_slice = obj.start is None and obj.stop is None
-            # could have integers in the first level of the MultiIndex
+
+            # could have integers in the first level of the MultiIndex,
+            # in which case we wouldn't want to do position-based slicing
             position_slice = (int_slice
                               and not ltype == 'integer'
-                              and not isinstance(labels, MultiIndex))
+                              and not isinstance(labels, MultiIndex)
+                              and not float_slice)
 
             start, stop = obj.start, obj.stop
 
             # last ditch effort: if we are mixed and have integers
             try:
-                if 'mixed' in ltype and int_slice:
+                if position_slice and 'mixed' in ltype:
                     if start is not None:
                         i = labels.get_loc(start)
                     if stop is not None:
@@ -468,7 +472,7 @@ def _convert_to_indexer(self, obj, axis=0):
                     indexer = labels.slice_indexer(start, stop, obj.step)
                 except Exception:
                     if _is_index_slice(obj):
-                        if labels.inferred_type == 'integer':
+                        if ltype == 'integer':
                             raise
                         indexer = obj
                     else:
@@ -539,34 +543,36 @@ def _get_slice_axis(self, slice_obj, axis=0):
 
         labels = obj._get_axis(axis)
 
-        int_slice = _is_index_slice(slice_obj)
-
-        start = slice_obj.start
-        stop = slice_obj.stop
+        ltype = labels.inferred_type
 
         # in case of providing all floats, use label-based indexing
         float_slice = (labels.inferred_type == 'floating'
                        and _is_float_slice(slice_obj))
 
+        # floats that are within tolerance of int used as positions
+        int_slice = _is_index_slice(slice_obj)
+
         null_slice = slice_obj.start is None and slice_obj.stop is None
 
-        # could have integers in the first level of the MultiIndex, in which
-        # case we wouldn't want to do position-based slicing
+        # could have integers in the first level of the MultiIndex,
+        # in which case we wouldn't want to do position-based slicing
         position_slice = (int_slice
-                          and labels.inferred_type != 'integer'
+                          and not ltype == 'integer'
                           and not isinstance(labels, MultiIndex)
                           and not float_slice)
 
+        start, stop = slice_obj.start, slice_obj.stop
+
         # last ditch effort: if we are mixed and have integers
         try:
-            if 'mixed' in labels.inferred_type and int_slice:
+            if position_slice and 'mixed' in ltype:
                 if start is not None:
                     i = labels.get_loc(start)
                 if stop is not None:
                     j = labels.get_loc(stop)
                 position_slice = False
         except KeyError:
-            if labels.inferred_type == 'mixed-integer-float':
+            if ltype == 'mixed-integer-float':
                 raise
 
         if null_slice or position_slice:
@@ -576,7 +582,7 @@ def _get_slice_axis(self, slice_obj, axis=0):
                 indexer = labels.slice_indexer(start, stop, slice_obj.step)
             except Exception:
                 if _is_index_slice(slice_obj):
-                    if labels.inferred_type == 'integer':
+                    if ltype == 'integer':
                         raise
                     indexer = slice_obj
                 else:

pandas/tests/test_frame.py

@@ -1183,6 +1183,45 @@ def test_getitem_setitem_float_labels(self):
         self.assertRaises(Exception, df.ix.__getitem__, slice(1, 2))
         self.assertRaises(Exception, df.ix.__setitem__, slice(1, 2), 0)
 
+        # #2727
+        index = Index([1.0, 2.5, 3.5, 4.5, 5.0])
+        df = DataFrame(np.random.randn(5, 5), index=index)
+
+        # positional slicing!
+        result = df.ix[1.0:5]
+        expected = df.reindex([2.5, 3.5, 4.5, 5.0])
+        assert_frame_equal(result, expected)
+        self.assertEqual(len(result), 4)
+
+        # positional again
+        result = df.ix[4:5]
+        expected = df.reindex([5.0])
+        assert_frame_equal(result, expected)
+        self.assertEqual(len(result), 1)
+
+        # label-based
+        result = df.ix[1.0:5.0]
+        expected = df.reindex([1.0, 2.5, 3.5, 4.5, 5.0])
+        assert_frame_equal(result, expected)
+        self.assertEqual(len(result), 5)
+    
+        cp = df.copy()
+        # positional slicing!
+        cp.ix[1.0:5] = 0
+        self.assert_((cp.ix[1.0:5] == 0).values.all())
+        self.assert_((cp.ix[0:1] == df.ix[0:1]).values.all())
+
+        cp = df.copy()
+        # positional again
+        cp.ix[4:5] = 0
+        self.assert_((cp.ix[4:5] == 0).values.all())
+        self.assert_((cp.ix[0:4] == df.ix[0:4]).values.all())
+        
+        cp = df.copy()
+        # label-based 
+        cp.ix[1.0:5.0] = 0
+        self.assert_((cp.ix[1.0:5.0] == 0).values.all())
+
     def test_setitem_single_column_mixed(self):
         df = DataFrame(randn(5, 3), index=['a', 'b', 'c', 'd', 'e'],
                        columns=['foo', 'bar', 'baz'])