BUG: Fix numpy boolean subtraction error in Series.diff (pandas-dev#28251)

Author: Unprocessable

doc/source/whatsnew/v1.0.0.rst

@@ -309,6 +309,7 @@ Other
 - Trying to set the ``display.precision``, ``display.max_rows`` or ``display.max_columns`` using :meth:`set_option` to anything but a ``None`` or a positive int will raise a ``ValueError`` (:issue:`23348`)
 - Using :meth:`DataFrame.replace` with overlapping keys in a nested dictionary will no longer raise, now matching the behavior of a flat dictionary (:issue:`27660`)
 - :meth:`DataFrame.to_csv` and :meth:`Series.to_csv` now support dicts as ``compression`` argument with key ``'method'`` being the compression method and others as additional compression options when the compression method is ``'zip'``. (:issue:`26023`)
+- Bug in :meth:`Series.diff` where a boolean series would incorrectly raise a ``TypeError`` (:issue:`17294`)
 - :meth:`Series.append` will no longer raise a ``TypeError`` when passed a tuple of ``Series`` (:issue:`28410`)
 
 .. _whatsnew_1000.contributors:

pandas/core/algorithms.py

@@ -1910,6 +1910,7 @@ def diff(arr, n: int, axis: int = 0):
     dtype = arr.dtype
 
     is_timedelta = False
+    is_bool = False
     if needs_i8_conversion(arr):
         dtype = np.float64
         arr = arr.view("i8")
@@ -1918,6 +1919,7 @@ def diff(arr, n: int, axis: int = 0):
 
     elif is_bool_dtype(dtype):
         dtype = np.object_
+        is_bool = True
 
     elif is_integer_dtype(dtype):
         dtype = np.float64
@@ -1959,6 +1961,8 @@ def diff(arr, n: int, axis: int = 0):
             result = res - lag
             result[mask] = na
             out_arr[res_indexer] = result
+        elif is_bool:
+            out_arr[res_indexer] = arr[res_indexer] ^ arr[lag_indexer]
         else:
             out_arr[res_indexer] = arr[res_indexer] - arr[lag_indexer]
 

pandas/tests/series/test_analytics.py

@@ -20,6 +20,7 @@
 from pandas.api.types import is_scalar
 from pandas.core.index import MultiIndex
 from pandas.core.indexes.datetimes import Timestamp
+from pandas.core.indexes.timedeltas import TimedeltaIndex
 import pandas.util.testing as tm
 from pandas.util.testing import (
     assert_almost_equal,
@@ -228,7 +229,7 @@ def test_cummax_timedelta64(self):
         result = s.cummax(skipna=False)
         tm.assert_series_equal(expected, result)
 
-    def test_npdiff(self):
+    def test_np_diff(self):
         pytest.skip("skipping due to Series no longer being an ndarray")
 
         # no longer works as the return type of np.diff is now nd.array
@@ -237,6 +238,67 @@ def test_npdiff(self):
         r = np.diff(s)
         assert_series_equal(Series([nan, 0, 0, 0, nan]), r)
 
+    def test_int_diff(self):
+        # int dtype
+        a = 10000000000000000
+        b = a + 1
+        s = Series([a, b])
+
+        result = s.diff()
+        assert result[1] == 1
+
+    def test_tz_diff(self):
+        # Combined datetime diff, normal diff and boolean diff test
+        ts = tm.makeTimeSeries(name="ts")
+        ts.diff()
+
+        # neg n
+        result = ts.diff(-1)
+        expected = ts - ts.shift(-1)
+        assert_series_equal(result, expected)
+
+        # 0
+        result = ts.diff(0)
+        expected = ts - ts
+        assert_series_equal(result, expected)
+
+        # datetime diff (GH3100)
+        s = Series(date_range("20130102", periods=5))
+        result = s.diff()
+        expected = s - s.shift(1)
+        assert_series_equal(result, expected)
+
+        # timedelta diff
+        result = result - result.shift(1)  # previous result
+        expected = expected.diff()  # previously expected
+        assert_series_equal(result, expected)
+
+        # with tz
+        s = Series(
+            date_range("2000-01-01 09:00:00", periods=5, tz="US/Eastern"), name="foo"
+        )
+        result = s.diff()
+        expected = Series(TimedeltaIndex(["NaT"] + ["1 days"] * 4), name="foo")
+        assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "input,output,diff",
+        [([False, True, True, False, False], [nan, True, False, True, False], 1)],
+    )
+    def test_bool_diff(self, input, output, diff):
+        # boolean series (test for fixing #17294)
+        s = Series(input)
+        result = s.diff()
+        expected = Series(output)
+        assert_series_equal(result, expected)
+
+    def test_obj_diff(self):
+        # object series
+        s = Series([False, True, 5.0, nan, True, False])
+        result = s.diff()
+        expected = s - s.shift(1)
+        assert_series_equal(result, expected)
+
     def _check_accum_op(self, name, datetime_series_, check_dtype=True):
         func = getattr(np, name)
         tm.assert_numpy_array_equal(

pandas/tests/series/test_timeseries.py

@@ -355,48 +355,6 @@ def test_asfreq_datetimeindex_empty_series(self):
         )
         tm.assert_index_equal(expected.index, result.index)
 
-    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()
-        assert rs[1] == 1
-
-        # neg n
-        rs = self.ts.diff(-1)
-        xp = self.ts - self.ts.shift(-1)
-        assert_series_equal(rs, xp)
-
-        # 0
-        rs = self.ts.diff(0)
-        xp = self.ts - self.ts
-        assert_series_equal(rs, xp)
-
-        # datetime diff (GH3100)
-        s = Series(date_range("20130102", periods=5))
-        rs = s - s.shift(1)
-        xp = s.diff()
-        assert_series_equal(rs, xp)
-
-        # timedelta diff
-        nrs = rs - rs.shift(1)
-        nxp = xp.diff()
-        assert_series_equal(nrs, nxp)
-
-        # with tz
-        s = Series(
-            date_range("2000-01-01 09:00:00", periods=5, tz="US/Eastern"), name="foo"
-        )
-        result = s.diff()
-        assert_series_equal(
-            result, Series(TimedeltaIndex(["NaT"] + ["1 days"] * 4), name="foo")
-        )
-
     def test_pct_change(self):
         rs = self.ts.pct_change(fill_method=None)
         assert_series_equal(rs, self.ts / self.ts.shift(1) - 1)