BUG: Make sure that head/tail are iloc based, (GH5370)

doc/source/release.rst

@@ -756,6 +756,7 @@ Bug Fixes
   - Test suite no longer leaves around temporary files when testing graphics. (:issue:`5347`)
     (thanks for catching this @yarikoptic!)
   - Fixed html tests on win32. (:issue:`4580`)
+  - Make sure that ``head/tail`` are ``iloc`` based, (:issue:`5370`)
 
 
 pandas 0.12.0

pandas/core/frame.py

@@ -3085,16 +3085,6 @@ def last_valid_index(self):
         """
         return self.index[self.count(1) > 0][-1]
 
-    def head(self, n=5):
-        """Returns first n rows of DataFrame
-        """
-        return self[:n]
-
-    def tail(self, n=5):
-        """Returns last n rows of DataFrame
-        """
-        return self[-n:]
-
     #----------------------------------------------------------------------
     # Data reshaping
 

pandas/core/generic.py

@@ -1461,6 +1461,24 @@ def filter(self, items=None, like=None, regex=None, axis=None):
         else:
             raise TypeError('Must pass either `items`, `like`, or `regex`')
 
+    def head(self, n=5):
+        """
+        Returns first n rows
+        """
+        l = len(self)
+        if abs(n) > l:
+            n = l if n > 0 else -l
+        return self.iloc[:n]
+
+    def tail(self, n=5):
+        """
+        Returns last n rows
+        """
+        l = len(self)
+        if abs(n) > l:
+            n = l if n > 0 else -l
+        return self.iloc[-n:]
+
     #----------------------------------------------------------------------
     # Attribute access
 

pandas/core/panel.py

@@ -581,6 +581,12 @@ def conform(self, frame, axis='items'):
         axes = self._get_plane_axes(axis)
         return frame.reindex(**self._extract_axes_for_slice(self, axes))
 
+    def head(self, n=5):
+        raise NotImplementedError
+
+    def tail(self, n=5):
+        raise NotImplementedError
+
     def _needs_reindex_multi(self, axes, method, level):
         # only allowing multi-index on Panel (and not > dims)
         return method is None and not self._is_mixed_type and self._AXIS_LEN <= 3 and com._count_not_none(*axes.values()) == 3

pandas/core/series.py

@@ -1058,16 +1058,6 @@ def to_sparse(self, kind='block', fill_value=None):
         return SparseSeries(self, kind=kind,
                             fill_value=fill_value).__finalize__(self)
 
-    def head(self, n=5):
-        """Returns first n rows of Series
-        """
-        return self[:n]
-
-    def tail(self, n=5):
-        """Returns last n rows of Series
-        """
-        return self[-n:]
-
     #----------------------------------------------------------------------
     # Statistics, overridden ndarray methods
 

pandas/tests/test_frame.py

@@ -4261,6 +4261,12 @@ def test_head_tail(self):
         assert_frame_equal(self.frame.head(), self.frame[:5])
         assert_frame_equal(self.frame.tail(), self.frame[-5:])
 
+        # with a float index
+        df = self.frame.copy()
+        df.index = np.arange(len(self.frame)) + 0.1
+        assert_frame_equal(df.head(), df.iloc[:5])
+        assert_frame_equal(df.tail(), df.iloc[-5:])
+
     def test_insert(self):
         df = DataFrame(np.random.randn(5, 3), index=np.arange(5),
                        columns=['c', 'b', 'a'])

pandas/tests/test_generic.py

@@ -317,6 +317,39 @@ def test_metadata_propagation(self):
             except (ValueError):
                 pass
 
+    def test_head_tail(self):
+        # GH5370
+
+        o = self._construct(shape=10)
+
+        # check all index types
+        for index in [ tm.makeFloatIndex, tm.makeIntIndex,
+                       tm.makeStringIndex, tm.makeUnicodeIndex,
+                       tm.makeDateIndex, tm.makePeriodIndex ]:
+            axis = o._get_axis_name(0)
+            setattr(o,axis,index(len(getattr(o,axis))))
+
+            # Panel + dims
+            try:
+                o.head()
+            except (NotImplementedError):
+                raise nose.SkipTest('not implemented on {0}'.format(o.__class__.__name__))
+
+            self._compare(o.head(), o.iloc[:5])
+            self._compare(o.tail(), o.iloc[-5:])
+
+            # 0-len
+            self._compare(o.head(0), o.iloc[:0])
+            self._compare(o.tail(0), o.iloc[0:])
+
+            # bounded
+            self._compare(o.head(len(o)+1), o)
+            self._compare(o.tail(len(o)+1), o)
+
+            # neg index
+            self._compare(o.head(-3), o.head(7))
+            self._compare(o.tail(-3), o.tail(7))
+
 class TestSeries(unittest.TestCase, Generic):
     _typ = Series
     _comparator = lambda self, x, y: assert_series_equal(x,y)