BUG: duplicate indexing with embedded non-orderables (#17610)

Author: gloryfromca

doc/source/whatsnew/v0.22.0.txt

@@ -294,6 +294,8 @@ Indexing
 - Bug in tz-aware :class:`DatetimeIndex` where addition/subtraction with a :class:`TimedeltaIndex` or array with ``dtype='timedelta64[ns]'`` was incorrect (:issue:`17558`)
 - :func:`Index.to_series` now accepts ``index`` and ``name`` kwargs (:issue:`18699`)
 - :func:`DatetimeIndex.to_series` now accepts ``index`` and ``name`` kwargs (:issue:`18699`)
+- Bug in indexing non-scalar value from ``Series`` having non-unique ``Index`` will return value flatted (:issue:`17610`)
+
 
 I/O
 ^^^

pandas/core/series.py

@@ -664,13 +664,15 @@ def __getitem__(self, key):
  if not is_scalar(result):
  if is_list_like(result) and not isinstance(result, Series):
 
- # we need to box if we have a non-unique index here
+ # we need to box if loc of the key isn't scalar here
  # otherwise have inline ndarray/lists
- if not self.index.is_unique:
- result = self._constructor(
- result, index=[key] * len(result),
- dtype=self.dtype).__finalize__(self)
-
+ try:
+ if not is_scalar(self.index.get_loc(key)):
+ result = self._constructor(
+ result, index=[key] * len(result),
+ dtype=self.dtype).__finalize__(self)
+ except KeyError:
+ pass
  return result
  except InvalidIndexError:
  pass

pandas/tests/series/test_indexing.py

@@ -547,6 +547,26 @@ def test_getitem_setitem_periodindex(self):
  result[4:8] = ts[4:8]
  assert_series_equal(result, ts)
 
+ @pytest.mark.parametrize(
+ 'result_1, duplicate_item, expected_1',
+ [
+ [
+ pd.Series({1: 12, 2: [1, 2, 2, 3]}), pd.Series({1: 313}),
+ pd.Series({1: 12, }, dtype=object),
+ ],
+ [
+ pd.Series({1: [1, 2, 3], 2: [1, 2, 2, 3]}),
+ pd.Series({1: [1, 2, 3]}), pd.Series({1: [1, 2, 3], }),
+ ],
+ ])
+ def test_getitem_with_duplicates_indices(
+ self, result_1, duplicate_item, expected_1):
+ # GH 17610
+ result = result_1.append(duplicate_item)
+ expected = expected_1.append(duplicate_item)
+ assert_series_equal(result[1], expected)
+ assert result[2] == result_1[2]
+
  def test_getitem_median_slice_bug(self):
  index = date_range('20090415', '20090519', freq='2B')
  s = Series(np.random.randn(13), index=index)