aboutsummaryrefslogtreecommitdiff
path: root/venv/lib/python3.8/site-packages/narwhals/_arrow/dataframe.py
blob: 19763b96062b244dd1ef333214ad80423dcfd020 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
from __future__ import annotations

from functools import partial
from typing import (
    TYPE_CHECKING,
    Any,
    Collection,
    Iterator,
    Literal,
    Mapping,
    Sequence,
    cast,
    overload,
)

import pyarrow as pa
import pyarrow.compute as pc

from narwhals._arrow.series import ArrowSeries
from narwhals._arrow.utils import align_series_full_broadcast, native_to_narwhals_dtype
from narwhals._compliant import EagerDataFrame
from narwhals._expression_parsing import ExprKind
from narwhals._utils import (
    Implementation,
    Version,
    check_column_names_are_unique,
    convert_str_slice_to_int_slice,
    generate_temporary_column_name,
    not_implemented,
    parse_columns_to_drop,
    parse_version,
    scale_bytes,
    supports_arrow_c_stream,
    validate_backend_version,
)
from narwhals.dependencies import is_numpy_array_1d
from narwhals.exceptions import ShapeError

if TYPE_CHECKING:
    from io import BytesIO
    from pathlib import Path
    from types import ModuleType

    import pandas as pd
    import polars as pl
    from typing_extensions import Self, TypeAlias, TypeIs

    from narwhals._arrow.expr import ArrowExpr
    from narwhals._arrow.group_by import ArrowGroupBy
    from narwhals._arrow.namespace import ArrowNamespace
    from narwhals._arrow.typing import (  # type: ignore[attr-defined]
        ChunkedArrayAny,
        Mask,
        Order,
    )
    from narwhals._compliant.typing import CompliantDataFrameAny, CompliantLazyFrameAny
    from narwhals._translate import IntoArrowTable
    from narwhals._utils import Version, _FullContext
    from narwhals.dtypes import DType
    from narwhals.schema import Schema
    from narwhals.typing import (
        JoinStrategy,
        SizedMultiIndexSelector,
        SizedMultiNameSelector,
        SizeUnit,
        UniqueKeepStrategy,
        _1DArray,
        _2DArray,
        _SliceIndex,
        _SliceName,
    )

    JoinType: TypeAlias = Literal[
        "left semi",
        "right semi",
        "left anti",
        "right anti",
        "inner",
        "left outer",
        "right outer",
        "full outer",
    ]
    PromoteOptions: TypeAlias = Literal["none", "default", "permissive"]


class ArrowDataFrame(EagerDataFrame["ArrowSeries", "ArrowExpr", "pa.Table"]):
    def __init__(
        self,
        native_dataframe: pa.Table,
        *,
        backend_version: tuple[int, ...],
        version: Version,
        validate_column_names: bool,
    ) -> None:
        if validate_column_names:
            check_column_names_are_unique(native_dataframe.column_names)
        self._native_frame = native_dataframe
        self._implementation = Implementation.PYARROW
        self._backend_version = backend_version
        self._version = version
        validate_backend_version(self._implementation, self._backend_version)

    @classmethod
    def from_arrow(cls, data: IntoArrowTable, /, *, context: _FullContext) -> Self:
        backend_version = context._backend_version
        if cls._is_native(data):
            native = data
        elif backend_version >= (14,) or isinstance(data, Collection):
            native = pa.table(data)
        elif supports_arrow_c_stream(data):  # pragma: no cover
            msg = f"'pyarrow>=14.0.0' is required for `from_arrow` for object of type {type(data).__name__!r}."
            raise ModuleNotFoundError(msg)
        else:  # pragma: no cover
            msg = f"`from_arrow` is not supported for object of type {type(data).__name__!r}."
            raise TypeError(msg)
        return cls.from_native(native, context=context)

    @classmethod
    def from_dict(
        cls,
        data: Mapping[str, Any],
        /,
        *,
        context: _FullContext,
        schema: Mapping[str, DType] | Schema | None,
    ) -> Self:
        from narwhals.schema import Schema

        pa_schema = Schema(schema).to_arrow() if schema is not None else schema
        native = pa.Table.from_pydict(data, schema=pa_schema)
        return cls.from_native(native, context=context)

    @staticmethod
    def _is_native(obj: pa.Table | Any) -> TypeIs[pa.Table]:
        return isinstance(obj, pa.Table)

    @classmethod
    def from_native(cls, data: pa.Table, /, *, context: _FullContext) -> Self:
        return cls(
            data,
            backend_version=context._backend_version,
            version=context._version,
            validate_column_names=True,
        )

    @classmethod
    def from_numpy(
        cls,
        data: _2DArray,
        /,
        *,
        context: _FullContext,
        schema: Mapping[str, DType] | Schema | Sequence[str] | None,
    ) -> Self:
        from narwhals.schema import Schema

        arrays = [pa.array(val) for val in data.T]
        if isinstance(schema, (Mapping, Schema)):
            native = pa.Table.from_arrays(arrays, schema=Schema(schema).to_arrow())
        else:
            native = pa.Table.from_arrays(arrays, cls._numpy_column_names(data, schema))
        return cls.from_native(native, context=context)

    def __narwhals_namespace__(self) -> ArrowNamespace:
        from narwhals._arrow.namespace import ArrowNamespace

        return ArrowNamespace(
            backend_version=self._backend_version, version=self._version
        )

    def __native_namespace__(self) -> ModuleType:
        if self._implementation is Implementation.PYARROW:
            return self._implementation.to_native_namespace()

        msg = f"Expected pyarrow, got: {type(self._implementation)}"  # pragma: no cover
        raise AssertionError(msg)

    def __narwhals_dataframe__(self) -> Self:
        return self

    def __narwhals_lazyframe__(self) -> Self:
        return self

    def _with_version(self, version: Version) -> Self:
        return self.__class__(
            self.native,
            backend_version=self._backend_version,
            version=version,
            validate_column_names=False,
        )

    def _with_native(self, df: pa.Table, *, validate_column_names: bool = True) -> Self:
        return self.__class__(
            df,
            backend_version=self._backend_version,
            version=self._version,
            validate_column_names=validate_column_names,
        )

    @property
    def shape(self) -> tuple[int, int]:
        return self.native.shape

    def __len__(self) -> int:
        return len(self.native)

    def row(self, index: int) -> tuple[Any, ...]:
        return tuple(col[index] for col in self.native.itercolumns())

    @overload
    def rows(self, *, named: Literal[True]) -> list[dict[str, Any]]: ...

    @overload
    def rows(self, *, named: Literal[False]) -> list[tuple[Any, ...]]: ...

    @overload
    def rows(self, *, named: bool) -> list[tuple[Any, ...]] | list[dict[str, Any]]: ...

    def rows(self, *, named: bool) -> list[tuple[Any, ...]] | list[dict[str, Any]]:
        if not named:
            return list(self.iter_rows(named=False, buffer_size=512))  # type: ignore[return-value]
        return self.native.to_pylist()

    def iter_columns(self) -> Iterator[ArrowSeries]:
        for name, series in zip(self.columns, self.native.itercolumns()):
            yield ArrowSeries.from_native(series, context=self, name=name)

    _iter_columns = iter_columns

    def iter_rows(
        self, *, named: bool, buffer_size: int
    ) -> Iterator[tuple[Any, ...]] | Iterator[dict[str, Any]]:
        df = self.native
        num_rows = df.num_rows

        if not named:
            for i in range(0, num_rows, buffer_size):
                rows = df[i : i + buffer_size].to_pydict().values()
                yield from zip(*rows)
        else:
            for i in range(0, num_rows, buffer_size):
                yield from df[i : i + buffer_size].to_pylist()

    def get_column(self, name: str) -> ArrowSeries:
        if not isinstance(name, str):
            msg = f"Expected str, got: {type(name)}"
            raise TypeError(msg)
        return ArrowSeries.from_native(self.native[name], context=self, name=name)

    def __array__(self, dtype: Any, *, copy: bool | None) -> _2DArray:
        return self.native.__array__(dtype, copy=copy)

    def _gather(self, rows: SizedMultiIndexSelector[ChunkedArrayAny]) -> Self:
        if len(rows) == 0:
            return self._with_native(self.native.slice(0, 0))
        if self._backend_version < (18,) and isinstance(rows, tuple):
            rows = list(rows)
        return self._with_native(self.native.take(rows))

    def _gather_slice(self, rows: _SliceIndex | range) -> Self:
        start = rows.start or 0
        stop = rows.stop if rows.stop is not None else len(self.native)
        if start < 0:
            start = len(self.native) + start
        if stop < 0:
            stop = len(self.native) + stop
        if rows.step is not None and rows.step != 1:
            msg = "Slicing with step is not supported on PyArrow tables"
            raise NotImplementedError(msg)
        return self._with_native(self.native.slice(start, stop - start))

    def _select_slice_name(self, columns: _SliceName) -> Self:
        start, stop, step = convert_str_slice_to_int_slice(columns, self.columns)
        return self._with_native(self.native.select(self.columns[start:stop:step]))

    def _select_slice_index(self, columns: _SliceIndex | range) -> Self:
        return self._with_native(
            self.native.select(self.columns[columns.start : columns.stop : columns.step])
        )

    def _select_multi_index(
        self, columns: SizedMultiIndexSelector[ChunkedArrayAny]
    ) -> Self:
        selector: Sequence[int]
        if isinstance(columns, pa.ChunkedArray):
            # TODO @dangotbanned: Fix upstream with `pa.ChunkedArray.to_pylist(self) -> list[Any]:`
            selector = cast("Sequence[int]", columns.to_pylist())
        # TODO @dangotbanned: Fix upstream, it is actually much narrower
        # **Doesn't accept `ndarray`**
        elif is_numpy_array_1d(columns):
            selector = columns.tolist()
        else:
            selector = columns
        return self._with_native(self.native.select(selector))

    def _select_multi_name(
        self, columns: SizedMultiNameSelector[ChunkedArrayAny]
    ) -> Self:
        selector: Sequence[str] | _1DArray
        if isinstance(columns, pa.ChunkedArray):
            # TODO @dangotbanned: Fix upstream with `pa.ChunkedArray.to_pylist(self) -> list[Any]:`
            selector = cast("Sequence[str]", columns.to_pylist())
        else:
            selector = columns
        # NOTE: Fixed in https://github.com/zen-xu/pyarrow-stubs/pull/221
        return self._with_native(self.native.select(selector))  # pyright: ignore[reportArgumentType]

    @property
    def schema(self) -> dict[str, DType]:
        schema = self.native.schema
        return {
            name: native_to_narwhals_dtype(dtype, self._version)
            for name, dtype in zip(schema.names, schema.types)
        }

    def collect_schema(self) -> dict[str, DType]:
        return self.schema

    def estimated_size(self, unit: SizeUnit) -> int | float:
        sz = self.native.nbytes
        return scale_bytes(sz, unit)

    explode = not_implemented()

    @property
    def columns(self) -> list[str]:
        return self.native.column_names

    def simple_select(self, *column_names: str) -> Self:
        return self._with_native(
            self.native.select(list(column_names)), validate_column_names=False
        )

    def select(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
        new_series = self._evaluate_into_exprs(*exprs)
        if not new_series:
            # return empty dataframe, like Polars does
            return self._with_native(
                self.native.__class__.from_arrays([]), validate_column_names=False
            )
        names = [s.name for s in new_series]
        reshaped = align_series_full_broadcast(*new_series)
        df = pa.Table.from_arrays([s.native for s in reshaped], names=names)
        return self._with_native(df, validate_column_names=True)

    def _extract_comparand(self, other: ArrowSeries) -> ChunkedArrayAny:
        length = len(self)
        if not other._broadcast:
            if (len_other := len(other)) != length:
                msg = f"Expected object of length {length}, got: {len_other}."
                raise ShapeError(msg)
            return other.native

        value = other.native[0]
        return pa.chunked_array([pa.repeat(value, length)])

    def with_columns(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
        # NOTE: We use a faux-mutable variable and repeatedly "overwrite" (native_frame)
        # All `pyarrow` data is immutable, so this is fine
        native_frame = self.native
        new_columns = self._evaluate_into_exprs(*exprs)
        columns = self.columns

        for col_value in new_columns:
            col_name = col_value.name
            column = self._extract_comparand(col_value)
            native_frame = (
                native_frame.set_column(columns.index(col_name), col_name, column=column)
                if col_name in columns
                else native_frame.append_column(col_name, column=column)
            )

        return self._with_native(native_frame, validate_column_names=False)

    def group_by(
        self, keys: Sequence[str] | Sequence[ArrowExpr], *, drop_null_keys: bool
    ) -> ArrowGroupBy:
        from narwhals._arrow.group_by import ArrowGroupBy

        return ArrowGroupBy(self, keys, drop_null_keys=drop_null_keys)

    def join(
        self,
        other: Self,
        *,
        how: JoinStrategy,
        left_on: Sequence[str] | None,
        right_on: Sequence[str] | None,
        suffix: str,
    ) -> Self:
        how_to_join_map: dict[str, JoinType] = {
            "anti": "left anti",
            "semi": "left semi",
            "inner": "inner",
            "left": "left outer",
            "full": "full outer",
        }

        if how == "cross":
            plx = self.__narwhals_namespace__()
            key_token = generate_temporary_column_name(
                n_bytes=8, columns=[*self.columns, *other.columns]
            )

            return self._with_native(
                self.with_columns(
                    plx.lit(0, None).alias(key_token).broadcast(ExprKind.LITERAL)
                )
                .native.join(
                    other.with_columns(
                        plx.lit(0, None).alias(key_token).broadcast(ExprKind.LITERAL)
                    ).native,
                    keys=key_token,
                    right_keys=key_token,
                    join_type="inner",
                    right_suffix=suffix,
                )
                .drop([key_token])
            )

        coalesce_keys = how != "full"  # polars full join does not coalesce keys
        return self._with_native(
            self.native.join(
                other.native,
                keys=left_on or [],  # type: ignore[arg-type]
                right_keys=right_on,  # type: ignore[arg-type]
                join_type=how_to_join_map[how],
                right_suffix=suffix,
                coalesce_keys=coalesce_keys,
            )
        )

    join_asof = not_implemented()

    def drop(self, columns: Sequence[str], *, strict: bool) -> Self:
        to_drop = parse_columns_to_drop(self, columns, strict=strict)
        return self._with_native(self.native.drop(to_drop), validate_column_names=False)

    def drop_nulls(self: ArrowDataFrame, subset: Sequence[str] | None) -> ArrowDataFrame:
        if subset is None:
            return self._with_native(self.native.drop_null(), validate_column_names=False)
        plx = self.__narwhals_namespace__()
        return self.filter(~plx.any_horizontal(plx.col(*subset).is_null()))

    def sort(self, *by: str, descending: bool | Sequence[bool], nulls_last: bool) -> Self:
        if isinstance(descending, bool):
            order: Order = "descending" if descending else "ascending"
            sorting: list[tuple[str, Order]] = [(key, order) for key in by]
        else:
            sorting = [
                (key, "descending" if is_descending else "ascending")
                for key, is_descending in zip(by, descending)
            ]

        null_placement = "at_end" if nulls_last else "at_start"

        return self._with_native(
            self.native.sort_by(sorting, null_placement=null_placement),
            validate_column_names=False,
        )

    def to_pandas(self) -> pd.DataFrame:
        return self.native.to_pandas()

    def to_polars(self) -> pl.DataFrame:
        import polars as pl  # ignore-banned-import

        return pl.from_arrow(self.native)  # type: ignore[return-value]

    def to_numpy(self, dtype: Any = None, *, copy: bool | None = None) -> _2DArray:
        import numpy as np  # ignore-banned-import

        arr: Any = np.column_stack([col.to_numpy() for col in self.native.columns])
        return arr

    @overload
    def to_dict(self, *, as_series: Literal[True]) -> dict[str, ArrowSeries]: ...

    @overload
    def to_dict(self, *, as_series: Literal[False]) -> dict[str, list[Any]]: ...

    def to_dict(
        self, *, as_series: bool
    ) -> dict[str, ArrowSeries] | dict[str, list[Any]]:
        it = self.iter_columns()
        if as_series:
            return {ser.name: ser for ser in it}
        return {ser.name: ser.to_list() for ser in it}

    def with_row_index(self, name: str) -> Self:
        df = self.native
        cols = self.columns

        row_indices = pa.array(range(df.num_rows))
        return self._with_native(
            df.append_column(name, row_indices).select([name, *cols])
        )

    def filter(
        self: ArrowDataFrame, predicate: ArrowExpr | list[bool | None]
    ) -> ArrowDataFrame:
        if isinstance(predicate, list):
            mask_native: Mask | ChunkedArrayAny = predicate
        else:
            # `[0]` is safe as the predicate's expression only returns a single column
            mask_native = self._evaluate_into_exprs(predicate)[0].native
        return self._with_native(
            self.native.filter(mask_native), validate_column_names=False
        )

    def head(self, n: int) -> Self:
        df = self.native
        if n >= 0:
            return self._with_native(df.slice(0, n), validate_column_names=False)
        else:
            num_rows = df.num_rows
            return self._with_native(
                df.slice(0, max(0, num_rows + n)), validate_column_names=False
            )

    def tail(self, n: int) -> Self:
        df = self.native
        if n >= 0:
            num_rows = df.num_rows
            return self._with_native(
                df.slice(max(0, num_rows - n)), validate_column_names=False
            )
        else:
            return self._with_native(df.slice(abs(n)), validate_column_names=False)

    def lazy(self, *, backend: Implementation | None = None) -> CompliantLazyFrameAny:
        if backend is None:
            return self
        elif backend is Implementation.DUCKDB:
            import duckdb  # ignore-banned-import

            from narwhals._duckdb.dataframe import DuckDBLazyFrame

            df = self.native  # noqa: F841
            return DuckDBLazyFrame(
                duckdb.table("df"),
                backend_version=parse_version(duckdb),
                version=self._version,
            )
        elif backend is Implementation.POLARS:
            import polars as pl  # ignore-banned-import

            from narwhals._polars.dataframe import PolarsLazyFrame

            return PolarsLazyFrame(
                cast("pl.DataFrame", pl.from_arrow(self.native)).lazy(),
                backend_version=parse_version(pl),
                version=self._version,
            )
        elif backend is Implementation.DASK:
            import dask  # ignore-banned-import
            import dask.dataframe as dd  # ignore-banned-import

            from narwhals._dask.dataframe import DaskLazyFrame

            return DaskLazyFrame(
                dd.from_pandas(self.native.to_pandas()),
                backend_version=parse_version(dask),
                version=self._version,
            )
        raise AssertionError  # pragma: no cover

    def collect(
        self, backend: Implementation | None, **kwargs: Any
    ) -> CompliantDataFrameAny:
        if backend is Implementation.PYARROW or backend is None:
            from narwhals._arrow.dataframe import ArrowDataFrame

            return ArrowDataFrame(
                self.native,
                backend_version=self._backend_version,
                version=self._version,
                validate_column_names=False,
            )

        if backend is Implementation.PANDAS:
            import pandas as pd  # ignore-banned-import

            from narwhals._pandas_like.dataframe import PandasLikeDataFrame

            return PandasLikeDataFrame(
                self.native.to_pandas(),
                implementation=Implementation.PANDAS,
                backend_version=parse_version(pd),
                version=self._version,
                validate_column_names=False,
            )

        if backend is Implementation.POLARS:
            import polars as pl  # ignore-banned-import

            from narwhals._polars.dataframe import PolarsDataFrame

            return PolarsDataFrame(
                cast("pl.DataFrame", pl.from_arrow(self.native)),
                backend_version=parse_version(pl),
                version=self._version,
            )

        msg = f"Unsupported `backend` value: {backend}"  # pragma: no cover
        raise AssertionError(msg)  # pragma: no cover

    def clone(self) -> Self:
        return self._with_native(self.native, validate_column_names=False)

    def item(self, row: int | None, column: int | str | None) -> Any:
        from narwhals._arrow.series import maybe_extract_py_scalar

        if row is None and column is None:
            if self.shape != (1, 1):
                msg = (
                    "can only call `.item()` if the dataframe is of shape (1, 1),"
                    " or if explicit row/col values are provided;"
                    f" frame has shape {self.shape!r}"
                )
                raise ValueError(msg)
            return maybe_extract_py_scalar(self.native[0][0], return_py_scalar=True)

        elif row is None or column is None:
            msg = "cannot call `.item()` with only one of `row` or `column`"
            raise ValueError(msg)

        _col = self.columns.index(column) if isinstance(column, str) else column
        return maybe_extract_py_scalar(self.native[_col][row], return_py_scalar=True)

    def rename(self, mapping: Mapping[str, str]) -> Self:
        names: dict[str, str] | list[str]
        if self._backend_version >= (17,):
            names = cast("dict[str, str]", mapping)
        else:  # pragma: no cover
            names = [mapping.get(c, c) for c in self.columns]
        return self._with_native(self.native.rename_columns(names))

    def write_parquet(self, file: str | Path | BytesIO) -> None:
        import pyarrow.parquet as pp

        pp.write_table(self.native, file)

    @overload
    def write_csv(self, file: None) -> str: ...

    @overload
    def write_csv(self, file: str | Path | BytesIO) -> None: ...

    def write_csv(self, file: str | Path | BytesIO | None) -> str | None:
        import pyarrow.csv as pa_csv

        if file is None:
            csv_buffer = pa.BufferOutputStream()
            pa_csv.write_csv(self.native, csv_buffer)
            return csv_buffer.getvalue().to_pybytes().decode()
        pa_csv.write_csv(self.native, file)
        return None

    def is_unique(self) -> ArrowSeries:
        col_token = generate_temporary_column_name(n_bytes=8, columns=self.columns)
        row_index = pa.array(range(len(self)))
        keep_idx = (
            self.native.append_column(col_token, row_index)
            .group_by(self.columns)
            .aggregate([(col_token, "min"), (col_token, "max")])
        )
        native = pa.chunked_array(
            pc.and_(
                pc.is_in(row_index, keep_idx[f"{col_token}_min"]),
                pc.is_in(row_index, keep_idx[f"{col_token}_max"]),
            )
        )
        return ArrowSeries.from_native(native, context=self)

    def unique(
        self: ArrowDataFrame,
        subset: Sequence[str] | None,
        *,
        keep: UniqueKeepStrategy,
        maintain_order: bool | None = None,
    ) -> ArrowDataFrame:
        # The param `maintain_order` is only here for compatibility with the Polars API
        # and has no effect on the output.
        import numpy as np  # ignore-banned-import

        if subset and (error := self._check_columns_exist(subset)):
            raise error
        subset = list(subset or self.columns)

        if keep in {"any", "first", "last"}:
            from narwhals._arrow.group_by import ArrowGroupBy

            agg_func = ArrowGroupBy._REMAP_UNIQUE[keep]
            col_token = generate_temporary_column_name(n_bytes=8, columns=self.columns)
            keep_idx_native = (
                self.native.append_column(col_token, pa.array(np.arange(len(self))))
                .group_by(subset)
                .aggregate([(col_token, agg_func)])
                .column(f"{col_token}_{agg_func}")
            )
            return self._with_native(
                self.native.take(keep_idx_native), validate_column_names=False
            )

        keep_idx = self.simple_select(*subset).is_unique()
        plx = self.__narwhals_namespace__()
        return self.filter(plx._expr._from_series(keep_idx))

    def gather_every(self, n: int, offset: int) -> Self:
        return self._with_native(self.native[offset::n], validate_column_names=False)

    def to_arrow(self) -> pa.Table:
        return self.native

    def sample(
        self,
        n: int | None,
        *,
        fraction: float | None,
        with_replacement: bool,
        seed: int | None,
    ) -> Self:
        import numpy as np  # ignore-banned-import

        num_rows = len(self)
        if n is None and fraction is not None:
            n = int(num_rows * fraction)
        rng = np.random.default_rng(seed=seed)
        idx = np.arange(0, num_rows)
        mask = rng.choice(idx, size=n, replace=with_replacement)
        return self._with_native(self.native.take(mask), validate_column_names=False)

    def unpivot(
        self,
        on: Sequence[str] | None,
        index: Sequence[str] | None,
        variable_name: str,
        value_name: str,
    ) -> Self:
        n_rows = len(self)
        index_ = [] if index is None else index
        on_ = [c for c in self.columns if c not in index_] if on is None else on
        concat = (
            partial(pa.concat_tables, promote_options="permissive")
            if self._backend_version >= (14, 0, 0)
            else pa.concat_tables
        )
        names = [*index_, variable_name, value_name]
        return self._with_native(
            concat(
                [
                    pa.Table.from_arrays(
                        [
                            *(self.native.column(idx_col) for idx_col in index_),
                            cast(
                                "ChunkedArrayAny",
                                pa.array([on_col] * n_rows, pa.string()),
                            ),
                            self.native.column(on_col),
                        ],
                        names=names,
                    )
                    for on_col in on_
                ]
            )
        )
        # TODO(Unassigned): Even with promote_options="permissive", pyarrow does not
        # upcast numeric to non-numeric (e.g. string) datatypes

    pivot = not_implemented()