polars.Expr.str.starts_with#

Expr.str.starts_with(prefix: str | Expr) → Expr[source]#

Check if string values start with a substring.

Parameters:

prefix: Prefix substring.

See also

contains: Check if string contains a substring that matches a regex.
ends_with: Check if string values end with a substring.

Examples

>>> df = pl.DataFrame({"fruits": ["apple", "mango", None]})
>>> df.with_columns(
...     pl.col("fruits").str.starts_with("app").alias("has_prefix"),
... )
shape: (3, 2)
┌────────┬────────────┐
│ fruits ┆ has_prefix │
│ ---    ┆ ---        │
│ str    ┆ bool       │
╞════════╪════════════╡
│ apple  ┆ true       │
│ mango  ┆ false      │
│ null   ┆ null       │
└────────┴────────────┘

>>> df = pl.DataFrame(
...     {"fruits": ["apple", "mango", "banana"], "prefix": ["app", "na", "ba"]}
... )
>>> df.with_columns(
...     pl.col("fruits").str.starts_with(pl.col("prefix")).alias("has_prefix"),
... )
shape: (3, 3)
┌────────┬────────┬────────────┐
│ fruits ┆ prefix ┆ has_prefix │
│ ---    ┆ ---    ┆ ---        │
│ str    ┆ str    ┆ bool       │
╞════════╪════════╪════════════╡
│ apple  ┆ app    ┆ true       │
│ mango  ┆ na     ┆ false      │
│ banana ┆ ba     ┆ true       │
└────────┴────────┴────────────┘

Using starts_with as a filter condition:

>>> df.filter(pl.col("fruits").str.starts_with("app"))
shape: (1, 2)
┌────────┬────────┐
│ fruits ┆ prefix │
│ ---    ┆ ---    │
│ str    ┆ str    │
╞════════╪════════╡
│ apple  ┆ app    │
└────────┴────────┘