BUG: correctly handle placement of pos/neg inf when dividing by integer 0 (GH6178)

Author: jreback

doc/source/release.rst

@@ -105,6 +105,7 @@ Bug Fixes
 - TimeGrouper has a more compatible API to the rest of the groupers (e.g. ``groups`` was missing) (:issue:`3881`)
 - Bug in ``pd.eval`` when parsing strings with possible tokens like ``'&'``
   (:issue:`6351`)
+- Bug correctly handle placements of ``-inf`` in Panels when dividing by integer 0 (:issue:`6359`)
 
 pandas 0.13.1
 -------------

pandas/core/common.py

@@ -1179,13 +1179,23 @@ def _lcd_dtypes(a_dtype, b_dtype):
     return np.object
 
 
-def _fill_zeros(result, y, fill):
-    """ if we have an integer value (or array in y)
+def _fill_zeros(result, x, y, name, fill):
+    """
+    if this is a reversed op, then flip x,y
+
+    if we have an integer value (or array in y)
     and we have 0's, fill them with the fill,
     return the result
+
+    mask the nan's from x
     """
 
     if fill is not None:
+
+        if name.startswith('r'):
+            x,y = y,x
+
+
         if not isinstance(y, np.ndarray):
             dtype, value = _infer_dtype_from_scalar(y)
             y = pa.empty(result.shape, dtype=dtype)
@@ -1196,8 +1206,18 @@ def _fill_zeros(result, y, fill):
             mask = y.ravel() == 0
             if mask.any():
                 shape = result.shape
-                result, changed = _maybe_upcast_putmask(
-                    result.ravel(), mask, fill)
+                result = result.ravel().astype('float64')
+
+                signs = np.sign(result)
+                nans = np.isnan(x.ravel())
+                np.putmask(result, mask & ~nans, fill)
+
+                # if we have a fill of inf, then sign it
+                # correctly
+                # GH 6178
+                if np.isinf(fill):
+                    np.putmask(result,signs<0 & mask & ~nans,-fill)
+
                 result = result.reshape(shape)
 
     return result

pandas/core/ops.py

@@ -454,7 +454,7 @@ def na_op(x, y):
 
             result, changed = com._maybe_upcast_putmask(result, -mask, pa.NA)
 
-        result = com._fill_zeros(result, y, fill_zeros)
+        result = com._fill_zeros(result, x, y, name, fill_zeros)
         return result
 
     def wrapper(left, right, name=name):
@@ -749,7 +749,7 @@ def na_op(x, y):
             result, changed = com._maybe_upcast_putmask(result, -mask, np.nan)
             result = result.reshape(x.shape)
 
-        result = com._fill_zeros(result, y, fill_zeros)
+        result = com._fill_zeros(result, x, y, name, fill_zeros)
 
         return result
 
@@ -913,7 +913,7 @@ def na_op(x, y):
             result[mask] = op(x[mask], y)
             result, changed = com._maybe_upcast_putmask(result, -mask, pa.NA)
 
-        result = com._fill_zeros(result, y, fill_zeros)
+        result = com._fill_zeros(result, x, y, name, fill_zeros)
         return result
 
     # work only for scalars

pandas/core/panel.py

@@ -1396,7 +1396,7 @@ def na_op(x, y):
                 # handles discrepancy between numpy and numexpr on division/mod
                 # by 0 though, given that these are generally (always?)
                 # non-scalars, I'm not sure whether it's worth it at the moment
-                result = com._fill_zeros(result, y, fill_zeros)
+                result = com._fill_zeros(result, x, y, name, fill_zeros)
                 return result
 
             @Substitution(name)

pandas/tests/test_panel.py

@@ -2071,23 +2071,20 @@ def test_arith_flex_panel(self):
         else:
             aliases = {'div': 'truediv'}
         self.panel = self.panel.to_panel()
-        n = np.random.randint(-50, 50)
-        for op in ops:
-            try:
+
+        for n in [ np.random.randint(-50, -1), np.random.randint(1, 50), 0]:
+            for op in ops:
                 alias = aliases.get(op, op)
                 f = getattr(operator, alias)
-                result = getattr(self.panel, op)(n)
                 exp = f(self.panel, n)
+                result = getattr(self.panel, op)(n)
                 assert_panel_equal(result, exp, check_panel_type=True)
 
                 # rops
                 r_f = lambda x, y: f(y, x)
-                result = getattr(self.panel, 'r' + op)(n)
                 exp = r_f(self.panel, n)
+                result = getattr(self.panel, 'r' + op)(n)
                 assert_panel_equal(result, exp)
-            except:
-                print("Failing operation %r" % op)
-                raise
 
     def test_sort(self):
         def is_sorted(arr):

pandas/tests/test_series.py

@@ -2212,6 +2212,12 @@ def test_div(self):
         assert_series_equal(result, p['first'].astype('float64'))
         self.assertFalse(np.array_equal(result, p['second'] / p['first']))
 
+        # inf signing
+        s = Series([np.nan,1.,-1.])
+        result = s / 0
+        expected = Series([np.nan,np.inf,-np.inf])
+        assert_series_equal(result, expected)
+
     def test_operators(self):
 
         def _check_op(series, other, op, pos_only=False):