BUG: fixes indexing with monotonic decreasing DTI (#19362)

Author: mapehe

doc/source/whatsnew/v0.23.0.txt

@@ -1077,6 +1077,7 @@ Indexing
 - Bug in :meth:`DataFrame.first_valid_index` and :meth:`DataFrame.last_valid_index` in presence of entire rows of NaNs in the middle of values (:issue:`20499`).
 - Bug in :class:`IntervalIndex` where some indexing operations were not supported for overlapping or non-monotonic ``uint64`` data (:issue:`20636`)
 - Bug in ``Series.is_unique`` where extraneous output in stderr is shown if Series contains objects with ``__ne__`` defined (:issue:`20661`)
+- Bug in indexing with monotonic decreasing datetimelike (:issue:`19362`)
 
 MultiIndex
 ^^^^^^^^^^

pandas/core/indexes/datetimelike.py

@@ -342,7 +342,8 @@ def _format_with_header(self, header, **kwargs):
  def __contains__(self, key):
  try:
  res = self.get_loc(key)
- return is_scalar(res) or type(res) == slice or np.any(res)
+ return (is_scalar(res) or isinstance(res, slice) or
+ (is_list_like(res) and len(res)))
  except (KeyError, TypeError, ValueError):
  return False
 

pandas/tests/indexes/datetimes/test_datetime.py

@@ -220,6 +220,27 @@ def test_groupby_function_tuple_1677(self):
  result = monthly_group.mean()
  assert isinstance(result.index[0], tuple)
 
+ def test_monotone_DTI_indexing_bug(self):
+ # GH 19362
+ # Testing accessing the first element of a montononic descending
+ # partial string indexing.
+
+ df = pd.DataFrame(list(range(5)))
+ date_list = ['2018-01-02', '2017-02-10', '2016-03-10',
+ '2015-03-15', '2014-03-16']
+ date_index = pd.to_datetime(date_list)
+ df['date'] = date_index
+ expected = pd.DataFrame({0: list(range(5)), 'date': date_index})
+ tm.assert_frame_equal(df, expected)
+
+ df = pd.DataFrame({'A': [1, 2, 3]},
+ index=pd.date_range('20170101',
+ periods=3)[::-1])
+ expected = pd.DataFrame({'A': 1},
+ index=pd.date_range('20170103',
+ periods=1))
+ tm.assert_frame_equal(df.loc['2017-01-03'], expected)
+
  def test_append_numpy_bug_1681(self):
  # another datetime64 bug
  dr = date_range('2011/1/1', '2012/1/1', freq='W-FRI')