Fix bug (GH17391)

Author: makbigc

doc/source/whatsnew/v0.25.0.rst

@@ -141,7 +141,7 @@ Datetimelike
 Timedelta
 ^^^^^^^^^
 
--
+- bug when TimedeltaIndex intersects with another decreasing TimedeltaIndex (:issue:`17391`) 
 -
 -
 

pandas/core/indexes/timedeltas.py

@@ -474,6 +474,10 @@ def intersection(self, other):
             return self
         if len(other) == 0:
             return other
+
+        self = self.sort_values()
+        other = other.sort_values()
+
         # to make our life easier, "sort" the two ranges
         if self[0] <= other[0]:
             left, right = self, other
@@ -486,7 +490,10 @@ def intersection(self, other):
         if end < start:
             return type(self)(data=[])
         else:
-            lslice = slice(*left.slice_locs(start, end))
+            lstart, lend = left.slice_locs(start, end)
+            lslice = np.arange(lstart, lend)
+            mask = [left_elem in right for left_elem in left[lstart: lend]]
+            lslice = lslice[mask]
             left_chunk = left.values[lslice]
             return self._shallow_copy(left_chunk)
 

pandas/tests/indexes/timedeltas/test_setops.py

@@ -1,4 +1,5 @@
 import numpy as np
+import pytest
 
 import pandas as pd
 from pandas import Int64Index, TimedeltaIndex, timedelta_range
@@ -73,3 +74,34 @@ def test_intersection_bug_1708(self):
         result = index_1 & index_2
         expected = timedelta_range('1 day 01:00:00', periods=3, freq='h')
         tm.assert_index_equal(result, expected)
+
+    @pytest.mark.parametrize('left, right, expected', [
+        (pd.to_timedelta(range(3), unit='s'),
+         pd.to_timedelta(range(2, -1, -1), unit='s'),
+         pd.to_timedelta(range(3), unit='s')),
+        (pd.to_timedelta(range(6, 3, -1), unit='s'),
+         pd.to_timedelta(range(5, 1, -1), unit='s'),
+         TimedeltaIndex(['00:00:04', '00:00:05'])),
+        (pd.to_timedelta(range(5, 1, -1), unit='s'),
+         pd.to_timedelta(range(6, 3, -1), unit='s'),
+         TimedeltaIndex(['00:00:04', '00:00:05'])),
+        (pd.to_timedelta((1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20), unit='s'),
+         pd.to_timedelta(range(1, 20), unit='s'),
+         pd.to_timedelta(range(1, 11), unit='s')),
+        (pd.to_timedelta((1, 2, 5, 6, 7), unit='s'),
+         pd.to_timedelta((3, 5, 6, 7), unit='s'),
+         pd.to_timedelta((5, 6, 7), unit='s'))
+    ])
+    def test_intersect(self, left, right, expected):
+        # GH 17391
+        result = left.intersection(right)
+        tm.assert_index_equal(result, expected)
+
+    @pytest.mark.parametrize('idx', [
+        pd.to_timedelta(range(1, 2), unit='s'),
+        pd.to_timedelta(range(2, -1, -1), unit='s')
+    ])
+    def test_intersect_self(self, idx):
+        # GH 17391
+        result = idx.intersection(idx)
+        tm.assert_index_equal(idx, result)