add code for analysis of data

1 files changed, 771 insertions, 0 deletions

diff --git a/venv/lib/python3.8/site-packages/narwhals/_arrow/dataframe.py b/venv/lib/python3.8/site-packages/narwhals/_arrow/dataframe.py
new file mode 100644
index 0000000..19763b9
--- /dev/null
+++ b/venv/lib/python3.8/site-packages/narwhals/_arrow/dataframe.py
@@ -0,0 +1,771 @@
+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()