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BUG: Respect dups in reindexing CategoricalIndex
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When the indexer is identical to the elements.
We should still return duplicates when the indexer
contains duplicates.

Closes pandas-devgh-17323.
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gfyoung committed Aug 28, 2017
1 parent 473a7f3 commit 13a5590
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Showing 3 changed files with 21 additions and 6 deletions.
1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.21.0.txt
Original file line number Diff line number Diff line change
Expand Up @@ -358,6 +358,7 @@ Indexing
- Allow unicode empty strings as placeholders in multilevel columns in Python 2 (:issue:`17099`)
- Bug in ``.iloc`` when used with inplace addition or assignment and an int indexer on a ``MultiIndex`` causing the wrong indexes to be read from and written to (:issue:`17148`)
- Bug in ``.isin()`` in which checking membership in empty ``Series`` objects raised an error (:issue:`16991`)
- Bug in ``CategoricalIndex`` reindexing in which specified indices containing duplicates were not being respected (:issue:`17323`)

I/O
^^^
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2 changes: 1 addition & 1 deletion pandas/core/indexes/category.py
Original file line number Diff line number Diff line change
Expand Up @@ -487,7 +487,7 @@ def get_indexer(self, target, method=None, limit=None, tolerance=None):
method = missing.clean_reindex_fill_method(method)
target = ibase._ensure_index(target)

if self.equals(target):
if self.is_unique and self.equals(target):
return np.arange(len(self), dtype='intp')

if method == 'pad' or method == 'backfill':
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24 changes: 19 additions & 5 deletions pandas/tests/indexes/test_category.py
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Expand Up @@ -365,18 +365,18 @@ def test_astype(self):
tm.assert_index_equal(result, expected)

def test_reindex_base(self):

# determined by cat ordering
idx = self.create_index()
# Determined by cat ordering.
idx = CategoricalIndex(list("cab"), categories=list("cab"))
expected = np.arange(len(idx), dtype=np.intp)

actual = idx.get_indexer(idx)
tm.assert_numpy_array_equal(expected, actual)

with tm.assert_raises_regex(ValueError, 'Invalid fill method'):
idx.get_indexer(idx, method='invalid')
with tm.assert_raises_regex(ValueError, "Invalid fill method"):
idx.get_indexer(idx, method="invalid")

def test_reindexing(self):
np.random.seed(123456789)

ci = self.create_index()
oidx = Index(np.array(ci))
Expand All @@ -388,6 +388,20 @@ def test_reindexing(self):
actual = ci.get_indexer(finder)
tm.assert_numpy_array_equal(expected, actual)

# see gh-17323
#
# Ensure that duplicate-handling is
# correct in general.
#
# In general, we want to make sure that
# re-indexing with indices identical to
# its members properly respect duplicates.
for finder in [list("aabbca"), list("aababca")]:
expected = oidx.get_indexer_non_unique(finder)[0]

actual = ci.get_indexer(finder)
tm.assert_numpy_array_equal(expected, actual)

def test_reindex_dtype(self):
c = CategoricalIndex(['a', 'b', 'c', 'a'])
res, indexer = c.reindex(['a', 'c'])
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