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BUG: reindex would throw when a categorical index was empty #16770 #16820

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3092bbc
BUG: reindex would throw when a categorical index was empty #16770
ri938 Jul 3, 2017
69454ec
Minor corrections to previous submit (#16820)
ri938 Jul 4, 2017
0a20024
Minor correction to previous submit
ri938 Jul 4, 2017
0645868
Add backticks in documentation
ri938 Jul 6, 2017
8f8e3d6
TST: register slow marker (#16797)
ri938 Jul 6, 2017
a725fbf
BUG: Fix read of py3 PeriodIndex DataFrame HDF made in py2 (#16781) (…
forbdonut Jun 30, 2017
800b40d
BUG: render dataframe as html do not produce duplicate element id's (…
ri938 Jul 3, 2017
5362447
fix BUG: ValueError when performing rolling covariance on multi index…
Jul 3, 2017
59b17cd
BUG: rolling.cov with multi-index columns should presever the MI (#16…
jreback Jul 4, 2017
26e1a60
Move documentation of change to the next major release 0.21.0
ri938 Jul 6, 2017
9ed80f0
Bring documentation into line with master branch.
ri938 Jul 7, 2017
6e8f1b3
Minor corrections to previous submit (#16820)
ri938 Jul 8, 2017
7acc09f
Minor correction to previous submit
ri938 Jul 4, 2017
eab3192
Merge branch 'master' into bug_issue16770
ri938 Jul 8, 2017
83fd749
Update v0.20.3.txt
ri938 Jul 18, 2017
1f2865e
Update v0.20.3.txt
ri938 Jul 18, 2017
9802288
Update v0.20.3.txt
ri938 Jul 18, 2017
0e2d315
Merge branch 'master' into bug_issue16770
ri938 Jul 18, 2017
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3 changes: 2 additions & 1 deletion doc/source/whatsnew/v0.20.3.txt
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Expand Up @@ -57,4 +57,5 @@ Reshaping
Categorical
^^^^^^^^^^^

- Bug in ``DataFrame.sort_values`` not respecting the ``kind`` parameter with categorical data (:issue:`16793`)

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revert this whatsnew note

- Bug in ``DataFrame.sort_values`` not respecting the ``kind`` with categorical data (:issue:`16793`)
1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.21.0.txt
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Expand Up @@ -141,6 +141,7 @@ Bug Fixes
~~~~~~~~~

- Fixes regression in 0.20, :func:`Series.aggregate` and :func:`DataFrame.aggregate` allow dictionaries as return values again (:issue:`16741`)
- Bug in reindexing on an empty ``CategoricalIndex`` (:issue:`16770`)

Conversion
^^^^^^^^^^
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7 changes: 5 additions & 2 deletions pandas/core/indexes/category.py
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Expand Up @@ -419,7 +419,11 @@ def reindex(self, target, method=None, level=None, limit=None,
raise ValueError("cannot reindex with a non-unique indexer")

indexer, missing = self.get_indexer_non_unique(np.array(target))
new_target = self.take(indexer)

if len(self.codes):
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if len(indexer)

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In the case the target is [1] say and the categorical index is empty then indexer here will be [-1] so not empty. The error occurs when try to run take on the empty underlying index.

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right its missing, so ok then.

new_target = self.take(indexer)
else:
new_target = target

# filling in missing if needed
if len(missing):
Expand All @@ -430,7 +434,6 @@ def reindex(self, target, method=None, level=None, limit=None,
result = Index(np.array(self), name=self.name)
new_target, indexer, _ = result._reindex_non_unique(
np.array(target))

else:

codes = new_target.codes.copy()
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8 changes: 8 additions & 0 deletions pandas/tests/indexes/test_category.py
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Expand Up @@ -419,6 +419,14 @@ def test_reindex_dtype(self):
tm.assert_numpy_array_equal(indexer,
np.array([0, 3, 2], dtype=np.intp))

def test_reindex_empty_index(self):
# See GH16770
c = CategoricalIndex([])
res, indexer = c.reindex(['a', 'b'])
tm.assert_index_equal(res, Index(['a', 'b']), exact=True)
tm.assert_numpy_array_equal(indexer,
np.array([-1, -1], dtype=np.intp))

def test_duplicates(self):

idx = CategoricalIndex([0, 0, 0], name='foo')
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