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Fix pivot index bug #37771

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Merged
merged 11 commits into from
Nov 14, 2020
Merged

Fix pivot index bug #37771

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46821e8
BUG: GH37635
Nov 11, 2020
9a7a60a
DOC: Documentation for GH37635
Nov 11, 2020
edebfaa
TST: Added test for GH37635
Nov 12, 2020
6fbebe4
TST: correct GH37635 test for code review
Nov 12, 2020
d673a9d
DOC: Corrected whats_new for GH37635
Nov 12, 2020
5833b33
CLN: newline at end of file
Nov 12, 2020
51acab0
BUG: Fixed regression in TestPivot.test_pivot_index_none
Nov 12, 2020
752ca20
TST: Code review on GH37635
Nov 12, 2020
4cff34b
TST: Code review on GH37635
Nov 12, 2020
2e249c9
TST: Code review on GH37635
Nov 12, 2020
9e9ed00
TST: code review GH37635
Nov 13, 2020
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.2.0.rst
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Expand Up @@ -553,6 +553,7 @@ Reshaping
- Bug in :meth:`DataFrame.agg` with ``func={'name':<FUNC>}`` incorrectly raising ``TypeError`` when ``DataFrame.columns==['Name']`` (:issue:`36212`)
- Bug in :meth:`Series.transform` would give incorrect results or raise when the argument ``func`` was dictionary (:issue:`35811`)
- Bug in :meth:`DataFrame.pivot` did not preserve :class:`MultiIndex` level names for columns when rows and columns both multiindexed (:issue:`36360`)
- Bug in :meth:`DataFrame.pivot` modified ``index`` argument when ``columns`` was passed but ``values`` was not (:issue:`37635`)
- Bug in :func:`join` returned a non deterministic level-order for the resulting :class:`MultiIndex` (:issue:`36910`)
- Bug in :meth:`DataFrame.combine_first()` caused wrong alignment with dtype ``string`` and one level of ``MultiIndex`` containing only ``NA`` (:issue:`37591`)
- Fixed regression in :func:`merge` on merging DatetimeIndex with empty DataFrame (:issue:`36895`)
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3 changes: 1 addition & 2 deletions pandas/core/reshape/pivot.py
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Expand Up @@ -450,10 +450,9 @@ def pivot(
cols = com.convert_to_list_like(index)
else:
cols = []
cols.extend(columns)

append = index is None
indexed = data.set_index(cols, append=append)
indexed = data.set_index(cols + columns, append=append)
else:
if index is None:
index = [Series(data.index, name=data.index.name)]
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37 changes: 37 additions & 0 deletions pandas/tests/reshape/test_pivot.py
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Expand Up @@ -2153,3 +2153,40 @@ def test_pivot_index_none(self):

expected.columns.name = "columns"
tm.assert_frame_equal(result, expected)

def test_pivot_index_list_values_none_modifies_args(self):
# GH37635
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@ivanovmg ivanovmg Nov 12, 2020 •
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This PR is about making sure that the index list does not change.
Would it be more reasonable to test here only that, without comparing pivoted table with the expected one?
This is related to one of your prior questions.

Thanks for the quick reply @arw2019!

Quick question: I'm essentially copying TestPivot.test_pivot(). The point of the bugfix is to prevent the pivot() method from modifying the passed argument index. Should I still include the assert statements from TestPivot.test_pivot() to verify that the pivot itself worked, or just include an assert statement focused on the bugfix?

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@Jacob-Stevens-Haas Jacob-Stevens-Haas Nov 12, 2020 •
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I had that originally, but a previous review asked that I

check here that you got the correct result from the pivot (might need to hard-code)

Doesn't much matter to me - now that the code is written, it's easy to delete or leave in as desired.

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I don't feel strongly on this
But I'd say it's useful to check that the pivot is doing what it's supposed to before checking that the args aren't changed

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I looked through the test module and noticed that there are no tests on pivot when index is a list and values are None.
Thus, there is no repetition of any kind and it is perfectly fine to have the test as it is.
Thank you!

df = DataFrame(
{
"lev1": [1, 1, 1, 2, 2, 2],
"lev2": [1, 1, 2, 1, 1, 2],
"lev3": [1, 2, 1, 2, 1, 2],
"lev4": [1, 2, 3, 4, 5, 6],
"values": [0, 1, 2, 3, 4, 5],
}
)
index = ["lev1", "lev2"]
columns = ["lev3"]
result = df.pivot(index=index, columns=columns, values=None)

expected = DataFrame(
np.array(
[
[1.0, 2.0, 0.0, 1.0],
[3.0, np.nan, 2.0, np.nan],
[5.0, 4.0, 4.0, 3.0],
[np.nan, 6.0, np.nan, 5.0],
]
),
index=MultiIndex.from_arrays(
[(1, 1, 2, 2), (1, 2, 1, 2)], names=["lev1", "lev2"]
),
columns=MultiIndex.from_arrays(
[("lev4", "lev4", "values", "values"), (1, 2, 1, 2)],
names=[None, "lev3"],
),
)

tm.assert_frame_equal(result, expected)

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check here that you got the correct result from the pivot (might need to hard-code)

assert index == ["lev1", "lev2"]
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can you also assert that columns is the same as original, ping on green.

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Done but not green; new comment below.

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I'd say it's green, LGTM

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@Jacob-Stevens-Haas Jacob-Stevens-Haas Nov 13, 2020 •
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Gotcha, thanks! @jreback?