59 lines
2.0 KiB
Python
59 lines
2.0 KiB
Python
from __future__ import annotations
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from typing import TYPE_CHECKING
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from typing import Generic
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from typing import TypeVar
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if TYPE_CHECKING:
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from typing_extensions import Self
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from narwhals.expr import Expr
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ExprT = TypeVar("ExprT", bound="Expr")
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class ExprStructNamespace(Generic[ExprT]):
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def __init__(self: Self, expr: ExprT) -> None:
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self._expr = expr
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def field(self: Self, name: str) -> ExprT:
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r"""Retrieve a Struct field as a new expression.
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Arguments:
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name: Name of the struct field to retrieve.
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Returns:
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A new expression.
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Examples:
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>>> import polars as pl
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>>> import narwhals as nw
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>>> df_native = pl.DataFrame(
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... {
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... "user": [
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... {"id": "0", "name": "john"},
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... {"id": "1", "name": "jane"},
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... ]
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... }
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... )
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>>> df = nw.from_native(df_native)
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>>> df.with_columns(name=nw.col("user").struct.field("name"))
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┌───────────────────────┐
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| Narwhals DataFrame |
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|-----------------------|
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|shape: (2, 2) |
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|┌──────────────┬──────┐|
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|│ user ┆ name │|
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|│ --- ┆ --- │|
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|│ struct[2] ┆ str │|
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|╞══════════════╪══════╡|
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|│ {"0","john"} ┆ john │|
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|│ {"1","jane"} ┆ jane │|
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|└──────────────┴──────┘|
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└───────────────────────┘
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"""
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return self._expr.__class__(
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lambda plx: self._expr._to_compliant_expr(plx).struct.field(name),
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self._expr._metadata,
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)
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