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BUG: pandas.DataFrame().stack() raise an error, while expected is empty #36185

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Merged
merged 28 commits into from
Nov 26, 2020
Merged

BUG: pandas.DataFrame().stack() raise an error, while expected is empty #36185

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165fd72
BUG: GH36113
steveya Sep 7, 2020
e0c1a8d
modify tests to avoid deprrecated errors
steveya Sep 7, 2020
f765acf
PEP 8 compliant
steveya Sep 7, 2020
109d312
remove trailing white space
steveya Sep 7, 2020
519a140
black format checked
steveya Sep 7, 2020
9d20ff5
DataFrame().stack should return an empty Series with dtype np.float64…
steveya Sep 9, 2020
d460db6
PEP8 again.
steveya Sep 9, 2020
bae2bd8
remove trailing space...\
steveya Sep 9, 2020
047ae40
add a comma to pass black lint
steveya Sep 9, 2020
c0fffe8
simply fixes and parameterize tests
steveya Sep 9, 2020
6b2b9bd
add error messages when unstack frame and series with single level index
steveya Sep 12, 2020
efc0603
apply ValueError location
steveya Sep 12, 2020
dac5f32
change the place where error is raised
steveya Sep 13, 2020
6524a6c
add a test for unstack series with one level of index. elaborate chan…
steveya Sep 16, 2020
6c71101
adding type information to exception message.
steveya Sep 22, 2020
e57aa51
Merge branch 'master' into GH36113
jreback Oct 10, 2020
f2f29bc
fix black format problem
steveya Oct 24, 2020
07d9ad5
resolve doc/source/whatsnew/v1.2.0.rst conflicts
steveya Nov 5, 2020
148b77d
fix unittest assert error message
steveya Nov 5, 2020
99f8280
change dtype of empty series and dataframe in test
steveya Nov 5, 2020
c4e244a
formatting
steveya Nov 5, 2020
668189f
change intp to int64 in testing of stack unstack empty frame
steveya Nov 20, 2020
20858db
Merge remote-tracking branch 'upstream/master' into GH36113
steveya Nov 20, 2020
4f95523
ensure indexer is of type int64
steveya Nov 22, 2020
7ab1155
Merge remote-tracking branch 'upstream/master' into GH36113
steveya Nov 25, 2020
475f158
remove xfail
steveya Nov 26, 2020
bdf49d3
remove unsed import
steveya Nov 26, 2020
f96453e
Merge remote-tracking branch 'upstream/master' into GH36113
steveya Nov 26, 2020
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.2.0.rst
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Expand Up @@ -322,7 +322,7 @@ Reshaping
- Bug in :meth:`DataFrame.pivot_table` with ``aggfunc='count'`` or ``aggfunc='sum'`` returning ``NaN`` for missing categories when pivoted on a ``Categorical``. Now returning ``0`` (:issue:`31422`)
- Bug in :func:`union_indexes` where input index names are not preserved in some cases. Affects :func:`concat` and :class:`DataFrame` constructor (:issue:`13475`)
- Bug in func :meth:`crosstab` when using multiple columns with ``margins=True`` and ``normalize=True`` (:issue:`35144`)
-
- Bug in :meth:`DataFrame.stack` for empty DataFrame (:issue:`36113`)
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can you elaborate a bit on what is changing.

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I have elaborate this a bit in the latest commit


Sparse
^^^^^^
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2 changes: 1 addition & 1 deletion pandas/core/reshape/reshape.py
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Expand Up @@ -517,7 +517,7 @@ def factorize(index):
# For homogeneous EAs, frame._values will coerce to object. So
# we concatenate instead.
dtypes = list(frame.dtypes._values)
dtype = dtypes[0]
dtype = dtypes[0] if len(dtypes) > 0 else object
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@ivanovmg ivanovmg Sep 8, 2020 •
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What if you return the Series right away if the dataframe is empty?

        if not frame.empty:
            dtypes = list(frame.dtypes._values)
            dtype = dtypes[0]
        else:
            return Series([], dtype=object)

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But you would still need to solve unstacking from an empty series.

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likely you can just add a not frame.empty and frame._is_homogenerous_type on L516 might work


if is_extension_array_dtype(dtype):
arr = dtype.construct_array_type()
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12 changes: 12 additions & 0 deletions pandas/tests/frame/test_reshape.py
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Expand Up @@ -1273,6 +1273,18 @@ def test_stack_timezone_aware_values():
tm.assert_series_equal(result, expected)


def test_stack_empty_frame():
tm.assert_series_equal(
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use

result=
expected=
tm.assert_series_equal (or frame)

pls parameterize these cases

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DataFrame().stack(),
Series(index=MultiIndex([[], []], [[], []]), dtype=np.float64),
)
tm.assert_series_equal(
DataFrame().stack(dropna=True),
Series(index=MultiIndex([[], []], [[], []]), dtype=np.float64),
)
tm.assert_frame_equal(DataFrame().stack().unstack(), DataFrame())


def test_unstacking_multi_index_df():
# see gh-30740
df = DataFrame(
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