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Series.value_counts: Preserve original ordering #24302

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Series.value_counts: Preserve original ordering #24302

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0270839
Series.value_counts: Preserve original ordering when using sort=False
tomspur Dec 21, 2018
c857119
Only reindex value_counts if bins is None
tomspur Dec 21, 2018
e966aa7
Modularize value_counts tests and xfail sort=True ones
tomspur Dec 23, 2018
b827df6
Move whatsnew entry to correct place
tomspur Dec 23, 2018
453d3df
Use ABCCategoricalIndex instead of CategoricalIndex
tomspur Dec 23, 2018
405ac0e
Calculate unique for the EA vs non-EA case
tomspur Dec 23, 2018
355f872
Parametrize value_counts test
tomspur Dec 23, 2018
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.24.0.rst
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Expand Up @@ -1634,6 +1634,7 @@ Other

- Bug where C variables were declared with external linkage causing import errors if certain other C libraries were imported before Pandas. (:issue:`24113`)
- Require at least 0.28.2 version of ``cython`` to support read-only memoryviews (:issue:`21688`)
- :meth:`Series.value_counts` returns the counts in the same ordering as the original series when using ``sort=False`` (:issue:`12679`)
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move to api breaking changes

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Done and pushed


.. _whatsnew_0.24.0.contributors:

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6 changes: 5 additions & 1 deletion pandas/core/algorithms.py
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Expand Up @@ -666,7 +666,7 @@ def value_counts(values, sort=True, ascending=False, normalize=False,
value_counts : Series

"""
from pandas.core.series import Series, Index
from pandas import Series, Index, CategoricalIndex
name = getattr(values, 'name', None)

if bins is not None:
Expand Down Expand Up @@ -708,6 +708,10 @@ def value_counts(values, sort=True, ascending=False, normalize=False,

if sort:
result = result.sort_values(ascending=ascending)
elif bins is None:
uniq = unique(values)
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so do
uniq = uniques(values) for the non-EA case (above)
and do uniq = Series(values)._values.unique() for the EA case. though this means computing it twice. maybe have to work on that.

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I added it above, although it is not computed twice now. Did you mean it like this?

if not isinstance(result.index, CategoricalIndex):
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why is this check needed? (or maybe it just needs to be for an ordered categorical)

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The issue was the test TestCategoricalSeriesAnalytics.test_value_counts:

cats = Categorical(list('abcccb'), categories=list('cabd'))
s = Series(cats, name='xxx')
res = s.value_counts(sort=False)

which returns 0 for the dcategory as well, which is not in the unique(values). Is there another possibility to get access to that initial categorical from the index?

result = result.reindex(uniq)

if normalize:
result = result / float(counts.sum())
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46 changes: 46 additions & 0 deletions pandas/tests/test_algos.py
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Expand Up @@ -962,6 +962,52 @@ def test_value_counts_uint64(self):
if not compat.is_platform_32bit():
tm.assert_series_equal(result, expected)

def test_value_counts_nonsorted_single_occurance(self):
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paramterize on sort

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Done and pushed

# GH 12679
# All items occour exactly once.
# No matter if sorted or not, the resulting values should be in
# the same order.
s = Series(list('bacdef'))

# Guarantee the same index if value_counts(sort=False) is used
vc = s.value_counts(sort=False, ascending=False)
tm.assert_series_equal(Series(vc.index), s)
vc = s.value_counts(sort=False, ascending=True)
tm.assert_series_equal(Series(vc.index), s)

@pytest.mark.xfail(reason="sort=True does not guarantee the same order")
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why is this xfail?

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I could not get it working for the sort=True case and left the tests only for possible future fixing... Would you prefer deleting them and adding them when sort=True works as well?

def test_value_counts_sorted_single_occurance(self):
# GH 12679
s = Series(list('bacdef'))
# Guarantee does not hold yet for the sort=True case
vc = s.value_counts(sort=True, ascending=False)
tm.assert_series_equal(Series(vc.index), s)
vc = s.value_counts(sort=True, ascending=True)
tm.assert_series_equal(Series(vc.index), s)

def test_value_counts_nonsorted_double_occurance(self):
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parametrize these.

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The double_occurance tests have different expected results and I wouldn't parametrize it due to that. Or would you do this as well in that case?

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I c, ok then, parameterize over ascending though

# GH 12679
# 'a' is there twice. Sorted, it should be there at the top.
s = Series(list('bacaef'))
ref_nonsorted = Series(list('bacef'))

# Guarantee the same index if value_counts(sort=False) is used
vc = s.value_counts(sort=False, ascending=False)
tm.assert_series_equal(Series(vc.index), ref_nonsorted)
vc = s.value_counts(sort=False, ascending=True)
tm.assert_series_equal(Series(vc.index), ref_nonsorted)

@pytest.mark.xfail(reason="sort=True does not guarantee the same order")
def test_value_counts_sorted_double_occurance(self):
# GH 12679
s = Series(list('bacaef'))
ref_sorted = Series(list('abcef'))
# Guarantee does not hold yet for the sort=True case
vc = s.value_counts(sort=True, ascending=False)
tm.assert_series_equal(Series(vc.index), ref_sorted)
vc = s.value_counts(sort=True, ascending=True)
tm.assert_series_equal(Series(vc.index), ref_sorted)


class TestDuplicated(object):

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