BUG: Series.diff for integer dtypes #2087

Author: changhiskhan

pandas/core/series.py

@@ -1511,7 +1511,22 @@ def diff(self, periods=1):
         -------
         diffed : Series
         """
-        return (self - self.shift(periods))
+        if com.is_integer_dtype(self):
+            new_values = np.empty(len(self), dtype=self.dtype)
+            new_values = _maybe_upcast(new_values)
+
+            if periods > 0:
+                new_values[periods:] = (self.values[periods:] -
+                                        self.values[:-periods])
+                new_values[:periods] = nan
+            elif periods < 0:
+                new_values[:periods] = (self.values[:periods] -
+                                        self.values[-periods:])
+                new_values[periods:] = nan
+
+            return Series(new_values, index=self.index, name=self.name)
+        else:
+            return self - self.shift(periods)
 
     def autocorr(self):
         """

pandas/tests/test_series.py

@@ -2998,6 +2998,14 @@ def test_diff(self):
         # Just run the function
         self.ts.diff()
 
+        # int dtype
+        a = 10000000000000000
+        b = a + 1
+        s = Series([a, b])
+
+        rs = s.diff()
+        self.assertEqual(rs[1], 1)
+
     def test_pct_change(self):
         rs = self.ts.pct_change(fill_method=None)
         assert_series_equal(rs, self.ts / self.ts.shift(1) - 1)