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Merged
merged 4 commits into from
Jan 4, 2023
Merged

ENH: Add lazy copy for truncate #50477

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bf16a0c
ENH: Add lazy copy for truncate
phofl Dec 28, 2022
8976062
Remove test
phofl Dec 29, 2022
6d100bb
Merge remote-tracking branch 'upstream/main' into cow_truncate
phofl Jan 3, 2023
b2c467c
Adjust condition
phofl Jan 3, 2023
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7 changes: 4 additions & 3 deletions pandas/core/generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,7 @@
SingleArrayManager,
)
from pandas.core.internals.construction import mgr_to_mgr
from pandas.core.internals.managers import _using_copy_on_write
from pandas.core.missing import (
clean_fill_method,
clean_reindex_fill_method,
Expand Down Expand Up @@ -9947,7 +9948,7 @@ def truncate(
before=None,
after=None,
axis: Axis | None = None,
copy: bool_t = True,
copy: bool_t | None = None,
) -> NDFrameT:
"""
Truncate a Series or DataFrame before and after some index value.
Expand Down Expand Up @@ -10098,8 +10099,8 @@ def truncate(
if isinstance(ax, MultiIndex):
setattr(result, self._get_axis_name(axis), ax.truncate(before, after))

if copy:
result = result.copy()
if copy or (copy is None and not _using_copy_on_write()):
result = result.copy(deep=copy)
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This might not be needed, since the result is from an indexing operation, and already should be a lazy copy (when using a slice) with refs set up

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We could rewrite as if copy or copy is None and _using_copy_on_write(), but we need the check for the non cow case

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Should it be if copy or (copy is None and not _using_copy_on_write())? (so with brackets and when not using CoW)

Essentially we need to same behaviour as this pattern that is used elsewhere, I think:

        if copy is None:
            if _using_copy_on_write():
                copy = False
            else:
                copy = True
        if copy:
            result = result.copy()

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Ah yes, forgot the not


return result

Expand Down
24 changes: 24 additions & 0 deletions pandas/tests/copy_view/test_methods.py
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Expand Up @@ -371,6 +371,30 @@ def test_head_tail(method, using_copy_on_write):
tm.assert_frame_equal(df, df_orig)


@pytest.mark.parametrize(
"kwargs",
[
{"before": "a", "after": "b", "axis": 1},
{"before": 0, "after": 1, "axis": 0},
],
)
def test_truncate(using_copy_on_write, kwargs):
df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 2})
df_orig = df.copy()
df2 = df.truncate(**kwargs)
df2._mgr._verify_integrity()

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"))

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", ["assign", "drop_duplicates"])
def test_assign_drop_duplicates(using_copy_on_write, method):
df = DataFrame({"a": [1, 2, 3]})
Expand Down
6 changes: 0 additions & 6 deletions pandas/tests/frame/methods/test_truncate.py
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Expand Up @@ -66,12 +66,6 @@ def test_truncate(self, datetime_frame, frame_or_series):
before=ts.index[-1] - ts.index.freq, after=ts.index[0] + ts.index.freq
)

def test_truncate_copy(self, datetime_frame):
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This is now covered in the cow tests

index = datetime_frame.index
truncated = datetime_frame.truncate(index[5], index[10])
truncated.values[:] = 5.0
assert not (datetime_frame.values[5:11] == 5).any()

def test_truncate_nonsortedindex(self, frame_or_series):
# GH#17935

Expand Down