polars.Expr.bin.starts_with#

Expr.bin.starts_with(prefix: IntoExpr) → Expr[source]#

Check if values start with a binary substring.

Parameters:

prefix: Prefix substring.

Returns:

Expr: Expression of data type Boolean.

See also

ends_with: Check if the binary substring exists at the end
contains: Check if the binary substring exists anywhere

Examples

>>> colors = pl.DataFrame(
...     {
...         "name": ["black", "yellow", "blue"],
...         "code": [b"\x00\x00\x00", b"\xff\xff\x00", b"\x00\x00\xff"],
...         "prefix": [b"\x00", b"\xff\x00", b"\x00\x00"],
...     }
... )
>>> colors.select(
...     "name",
...     pl.col("code").bin.starts_with(b"\xff").alias("starts_with_lit"),
...     pl.col("code")
...     .bin.starts_with(pl.col("prefix"))
...     .alias("starts_with_expr"),
... )
shape: (3, 3)
┌────────┬─────────────────┬──────────────────┐
│ name   ┆ starts_with_lit ┆ starts_with_expr │
│ ---    ┆ ---             ┆ ---              │
│ str    ┆ bool            ┆ bool             │
╞════════╪═════════════════╪══════════════════╡
│ black  ┆ false           ┆ true             │
│ yellow ┆ true            ┆ false            │
│ blue   ┆ false           ┆ true             │
└────────┴─────────────────┴──────────────────┘