BUG: Rolling negative window issue fix #13383

Author: priyankjain

doc/source/whatsnew/v0.18.2.txt

@@ -516,3 +516,4 @@ Bug Fixes
 
 
 - Bug in ``Categorical.remove_unused_categories()`` changes ``.codes`` dtype to platform int (:issue:`13261`)
+- Bug in ``Series.rolling()`` that allowed negative window, but failed on aggregation (:issue:`13383`)

pandas/core/window.py

@@ -321,6 +321,8 @@ def validate(self):
         if isinstance(window, (list, tuple, np.ndarray)):
             pass
         elif com.is_integer(window):
+            if window < 0:
+                raise ValueError("window must be non-negative")
             try:
                 import scipy.signal as sig
             except ImportError:
@@ -850,6 +852,8 @@ def validate(self):
         super(Rolling, self).validate()
         if not com.is_integer(self.window):
             raise ValueError("window must be an integer")
+        elif self.window < 0:
+            raise ValueError("window must be non-negative")
 
     @Substitution(name='rolling')
     @Appender(SelectionMixin._see_also_template)

pandas/tests/test_window.py

@@ -331,6 +331,11 @@ def test_constructor(self):
             c(window=2, min_periods=1, center=True)
             c(window=2, min_periods=1, center=False)
 
+            # GH 13383
+            c(0)
+            with self.assertRaises(ValueError):
+                c(-1)
+
             # not valid
             for w in [2., 'foo', np.array([2])]:
                 with self.assertRaises(ValueError):
@@ -340,6 +345,15 @@ def test_constructor(self):
                 with self.assertRaises(ValueError):
                     c(window=2, min_periods=1, center=w)
 
+    def test_constructor_with_win_type(self):
+        # GH 13383
+        tm._skip_if_no_scipy()
+        for o in [self.series, self.frame]:
+            c = o.rolling
+            c(0, win_type='boxcar')
+            with self.assertRaises(ValueError):
+                c(-1, win_type='boxcar')
+
     def test_numpy_compat(self):
         # see gh-12811
         r = rwindow.Rolling(Series([2, 4, 6]), window=2)