Types

Function	Description
CAST	Convert a value to a different datatype.
TRY_CAST	Convert a value to a different datatype, returning NULL if the conversion fails.

CAST

Convert a value to a different datatype.

Note that the more compact PostgreSQL <expr>::type syntax is also supported.

Example:

df = pl.DataFrame(
  {
    "foo": [20, 10, 30],
    "bar": ["1999-12-31", "2012-07-05", "2024-01-01"],
  }
)
df.sql("""
  SELECT
    foo::float4,
    bar::date
  FROM self
""")
# shape: (3, 2)
# ┌──────┬────────────┐
# │ foo  ┆ bar        │
# │ ---  ┆ ---        │
# │ f32  ┆ date       │
# ╞══════╪════════════╡
# │ 20.0 ┆ 1999-12-31 │
# │ 10.0 ┆ 2012-07-05 │
# │ 30.0 ┆ 2024-01-01 │
# └──────┴────────────┘

TRY_CAST

Convert a value to a different datatype, returning NULL if the conversion fails.

Example:

df = pl.DataFrame(
  {
    "foo": [65432, 10101, -33333],
    "bar": ["1999-12-31", "N/A", "2024-01-01"],
  }
)
df.sql("""
  SELECT
    TRY_CAST(foo AS uint2),
    TRY_CAST(bar AS date)
  FROM self
""")
# shape: (3, 2)
# ┌───────┬────────────┐
# │ foo   ┆ bar        │
# │ ---   ┆ ---        │
# │ u16   ┆ date       │
# ╞═══════╪════════════╡
# │ 65432 ┆ 1999-12-31 │
# │ 10101 ┆ null       │
# │ null  ┆ 2024-01-01 │
# └───────┴────────────┘

Note that with a regular CAST this would fail with the following error:

InvalidOperationError:
  conversion from `i64` to `u16` failed in column 'foo' for 1 out of 3 values: [-33333]