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ENH: Add copy-on-write to DataFrame.drop #49689

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Merged
merged 4 commits into from
Nov 16, 2022
Merged

ENH: Add copy-on-write to DataFrame.drop #49689

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92f5707
ENH/TST: add CoW to df.drop and test for it GH49473
seljaks Nov 13, 2022
36a2b51
black
seljaks Nov 14, 2022
d2d47b0
fix mypy error
seljaks Nov 14, 2022
b32e606
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seljaks Nov 15, 2022
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1 change: 1 addition & 0 deletions pandas/core/generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4483,6 +4483,7 @@ def _drop_axis(
indexer,
axis=bm_axis,
allow_dups=True,
copy=None,
only_slice=only_slice,
)
result = self._constructor(new_mgr)
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4 changes: 2 additions & 2 deletions pandas/core/internals/array_manager.py
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Expand Up @@ -546,7 +546,7 @@ def reindex_indexer(
axis: AxisInt,
fill_value=None,
allow_dups: bool = False,
copy: bool = True,
copy: bool | None = True,
# ignored keywords
only_slice: bool = False,
# ArrayManager specific keywords
Expand All @@ -570,7 +570,7 @@ def _reindex_indexer(
axis: AxisInt,
fill_value=None,
allow_dups: bool = False,
copy: bool = True,
copy: bool | None = True,
use_na_proxy: bool = False,
) -> T:
"""
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18 changes: 18 additions & 0 deletions pandas/tests/copy_view/test_methods.py
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Expand Up @@ -52,6 +52,24 @@ def test_copy_shallow(using_copy_on_write):
# DataFrame methods returning new DataFrame using shallow copy


def test_drop_on_column(using_copy_on_write):
df = DataFrame(
{"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=[10, 11, 12]
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Suggested change
{"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=[10, 11, 12]
{"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}

(I used a custom index for the reset_index test, but for the drop test, a custom index shouldn't matter)

)
df_orig = df.copy()
df2 = df.drop(columns="a")
df2._mgr._verify_integrity()

if using_copy_on_write:
assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
df2.iloc[0, 0] = 0
assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
if using_copy_on_write:
assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
tm.assert_frame_equal(df, df_orig)


def test_reset_index(using_copy_on_write):
# Case: resetting the index (i.e. adding a new column) + mutating the
# resulting dataframe
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