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ENH: Add lazy copy for swapaxes no op #50573

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Merged
merged 7 commits into from
Jan 12, 2023
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ENH: Add lazy copy for swapaxes no op #50573

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ENH: Add lazy copy for swapaxes no op
phofl Jan 4, 2023
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Move condition
phofl Jan 5, 2023
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Merge branch 'main' into cow_swapapxes
phofl Jan 6, 2023
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Merge remote-tracking branch 'upstream/main' into cow_swapapxes
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Add single block case
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Fix typing
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Merge remote-tracking branch 'upstream/main' into cow_swapapxes
phofl Jan 12, 2023
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8 changes: 4 additions & 4 deletions pandas/core/generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -761,7 +761,7 @@ def _set_axis(self, axis: AxisInt, labels: AnyArrayLike | list) -> None:

@final
def swapaxes(
self: NDFrameT, axis1: Axis, axis2: Axis, copy: bool_t = True
self: NDFrameT, axis1: Axis, axis2: Axis, copy: bool_t | None = None
) -> NDFrameT:
"""
Interchange axes and swap values axes appropriately.
Expand All @@ -774,9 +774,9 @@ def swapaxes(
j = self._get_axis_number(axis2)

if i == j:
if copy:
return self.copy()
return self
if not copy and copy is not None and not _using_copy_on_write():
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Suggested change
if not copy and copy is not None and not _using_copy_on_write():
if copy is False and not _using_copy_on_write():

return self
return self.copy(deep=copy)

mapping = {i: j, j: i}

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18 changes: 18 additions & 0 deletions pandas/tests/copy_view/test_methods.py
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Expand Up @@ -255,6 +255,24 @@ def test_to_frame(using_copy_on_write):
tm.assert_frame_equal(df, expected)


@pytest.mark.parametrize("ax", ["index", "columns"])
def test_swapaxes_noop(using_copy_on_write, ax):
df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
df_orig = df.copy()
df2 = df.swapaxes(ax, ax)

if using_copy_on_write:
assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
else:
assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))

# mutating df2 triggers a copy-on-write for that column/block
df2.iloc[0, 0] = 0
if using_copy_on_write:
assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
tm.assert_frame_equal(df, df_orig)


@pytest.mark.parametrize(
"method, idx",
[
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