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BUG: astype to pyarrow does not copy np array #50984

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Merged
merged 3 commits into from
Jan 30, 2023
Merged

BUG: astype to pyarrow does not copy np array #50984

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c91c5b9
BUG: astype to pyarrow does not copy np array
phofl Jan 26, 2023
6df179e
Add gh ref
phofl Jan 26, 2023
8defadf
Use deepcopy
phofl Jan 26, 2023
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.0.0.rst
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Expand Up @@ -1015,6 +1015,7 @@ Conversion
- Bug in :class:`.arrays.ArrowExtensionArray` that would raise ``NotImplementedError`` when passed a sequence of strings or binary (:issue:`49172`)
- Bug in :meth:`Series.astype` raising ``pyarrow.ArrowInvalid`` when converting from a non-pyarrow string dtype to a pyarrow numeric type (:issue:`50430`)
- Bug in :meth:`Series.to_numpy` converting to NumPy array before applying ``na_value`` (:issue:`48951`)
- Bug in :meth:`DataFrame.astype` not copying data when converting to pyarrow dtype (:issue:`50984`)
- Bug in :func:`to_datetime` was not respecting ``exact`` argument when ``format`` was an ISO8601 format (:issue:`12649`)
- Bug in :meth:`TimedeltaArray.astype` raising ``TypeError`` when converting to a pyarrow duration type (:issue:`49795`)
-
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3 changes: 3 additions & 0 deletions pandas/core/arrays/arrow/array.py
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Expand Up @@ -218,6 +218,9 @@ def _from_sequence(cls, scalars, *, dtype: Dtype | None = None, copy: bool = Fal
if isinstance(scalars, cls):
scalars = scalars._data
elif not isinstance(scalars, (pa.Array, pa.ChunkedArray)):
if copy and is_array_like(scalars):
# pa array should not get updated when numpy array is updated
scalars = scalars.copy()
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Is it worth specifying np.array(scalars, copy=True) manually? There might be an off chance the arraylike doesn't have a copy method?

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This would cast our nullables to object, so not ideal

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Ah gotcha. Would calling copy.copy(...) be safer then?

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We need deepcopy, but this should do the trick

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There might be an off chance the arraylike doesn't have a copy method?

might make more sense to raise than guess if this occurs?

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No preference here, cc @mroeschke

try:
scalars = pa.array(scalars, type=pa_dtype, from_pandas=True)
except pa.ArrowInvalid:
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12 changes: 12 additions & 0 deletions pandas/tests/frame/methods/test_astype.py
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Expand Up @@ -3,6 +3,7 @@
import numpy as np
import pytest

from pandas.compat import pa_version_under6p0
import pandas.util._test_decorators as td

import pandas as pd
Expand Down Expand Up @@ -867,3 +868,14 @@ def test_frame_astype_no_copy():

assert result.a.dtype == pd.Int16Dtype()
assert np.shares_memory(df.b.values, result.b.values)


@pytest.mark.skipif(pa_version_under6p0, reason="pyarrow is required for this test")
@pytest.mark.parametrize("dtype", ["int64", "Int64"])
def test_astype_copies(dtype):
# GH#50984
df = DataFrame({"a": [1, 2, 3]}, dtype=dtype)
result = df.astype("int64[pyarrow]", copy=True)
df.iloc[0, 0] = 100
expected = DataFrame({"a": [1, 2, 3]}, dtype="int64[pyarrow]")
tm.assert_frame_equal(result, expected)