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feat: allow passing Series to Series.__getitem__ #1533

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feat: allow passing Series to Series.__getitem__ #1533

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53de4f3
enh: allow passing Series to Series.__getitem__.
devdanzin Dec 7, 2024
9f0139c
Address pre-commit issues.
devdanzin Dec 7, 2024
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13 changes: 9 additions & 4 deletions narwhals/_polars/series.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@

from narwhals._polars.dataframe import PolarsDataFrame
from narwhals.dtypes import DType
from narwhals.series import Series as NWSeries
from narwhals.utils import Version

T = TypeVar("T")
Expand Down Expand Up @@ -120,10 +121,14 @@ def dtype(self: Self) -> DType:
def __getitem__(self: Self, item: int) -> Any: ...

@overload
def __getitem__(self: Self, item: slice | Sequence[int]) -> Self: ...

def __getitem__(self: Self, item: int | slice | Sequence[int]) -> Any | Self:
return self._from_native_object(self._native_series.__getitem__(item))
def __getitem__(self: Self, item: slice | Sequence[int] | NWSeries[Any]) -> Self: ...

def __getitem__(
self: Self, item: int | slice | Sequence[int] | NWSeries[Any]
) -> Any | Self:
if isinstance(item, (int, slice, Sequence)):
return self._from_native_object(self._native_series.__getitem__(item))
return self._from_native_object(self._native_series.__getitem__(item.to_numpy()))
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@MarcoGorelli MarcoGorelli Dec 7, 2024 •
edited
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🤔 not sure we should be converting to numpy here

I'm not totally sure what we should be doing instead though, sorry, will need to investigate

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Thank you, I had doubts about this too and picked a solution that seemed to work without actually understanding the consequences.

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It seems using item.to_native() instead works, and also solves an issue with missing values becoming NaN with to_numpy(). Do you think it's acceptable? Any other corner cases to cover with tests?

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thanks - i'll check, to be careful we get the details right here


def cast(self: Self, dtype: DType) -> Self:
ser = self._native_series
Expand Down
6 changes: 4 additions & 2 deletions narwhals/series.py
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Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,11 @@ def __array__(self: Self, dtype: Any = None, copy: bool | None = None) -> np.nda
def __getitem__(self: Self, idx: int) -> Any: ...

@overload
def __getitem__(self: Self, idx: slice | Sequence[int]) -> Self: ...
def __getitem__(self: Self, idx: slice | Sequence[int] | Series[Any]) -> Self: ...

def __getitem__(self: Self, idx: int | slice | Sequence[int]) -> Any | Self:
def __getitem__(
self: Self, idx: int | slice | Sequence[int] | Series[Any]
) -> Any | Self:
if isinstance(idx, int):
return self._compliant_series[idx]
return self._from_compliant_series(self._compliant_series[idx])
Expand Down
18 changes: 18 additions & 0 deletions tests/series_only/__getitem___test.py
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@@ -0,0 +1,18 @@
from __future__ import annotations

import polars as pl
import pytest

import narwhals.stable.v1 as nw


def test_getitem() -> None:
spl = pl.Series([1, 2, 3])
assert spl[spl[0, 1]].equals(pl.Series([2, 3]))
Comment on lines +10 to +11
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can we check what happens when there's missing values too please?

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Using to_native() instead of to_numpy() allows the following tests to pass, but my complete lack of knowledge on numpy, narwhals, polars and related subjects makes me unsure they are correct and show expected behavior:

    spl = pl.Series([1, None, 3])
    assert spl[spl[0, 1]].equals(pl.Series([None, None]))

    snw = nw.from_native(spl, series_only=True)
    assert snw[snw[0, 1]].to_native().equals(pl.Series([None, None]))

What's your take on this?


snw = nw.from_native(spl, series_only=True)
assert snw[snw[0, 1]].to_native().equals(pl.Series([2, 3]))

spl = pl.Series([1, 2, 3])
snw = nw.from_native(spl, series_only=True)
assert pytest.raises(TypeError, lambda: snw[snw[True, False]])
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