Casts an expression to the given datatype if possible.
See the casting matrix for supported casts.
Returns:
| Name | Type | Description |
Expression | Expression | Expression with the specified new datatype |
Note
- If a string is provided, it will use the sql engine to parse the string into a data type. See the SQL Reference for supported datatypes.
- a python
type can also be provided, in which case the corresponding Daft data type will be used.
See Also
Expression.cast
Examples:
| >>> import daft
>>> df = daft.from_pydict({"float": [1.0, 2.5, None]})
>>> df = df.select(df["float"].cast(daft.DataType.int64()))
>>> df.show()
|
╭───────╮
│ float │
│ --- │
│ Int64 │
╞═══════╡
│ 1 │
├╌╌╌╌╌╌╌┤
│ 2 │
├╌╌╌╌╌╌╌┤
│ None │
╰───────╯
(Showing first 3 of 3 rows)
Example with python type and sql types:
| >>> df = daft.from_pydict({"a": [1, 2, 3]})
>>> df = df.select(
... df["a"].cast(str).alias("str"),
... df["a"].cast(int).alias("int"),
... df["a"].cast(float).alias("float"),
... df["a"].cast("string").alias("sql_string"),
... df["a"].cast("int").alias("sql_int"),
... df["a"].cast("tinyint").alias("sql_tinyint"),
... )
>>> df.show()
|
╭────────┬───────┬─────────┬────────────┬─────────┬─────────────╮
│ str ┆ int ┆ float ┆ sql_string ┆ sql_int ┆ sql_tinyint │
│ --- ┆ --- ┆ --- ┆ --- ┆ --- ┆ --- │
│ String ┆ Int64 ┆ Float64 ┆ String ┆ Int32 ┆ Int8 │
╞════════╪═══════╪═════════╪════════════╪═════════╪═════════════╡
│ 1 ┆ 1 ┆ 1 ┆ 1 ┆ 1 ┆ 1 │
├╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ 2 ┆ 2 ┆ 2 ┆ 2 ┆ 2 ┆ 2 │
├╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ 3 ┆ 3 ┆ 3 ┆ 3 ┆ 3 ┆ 3 │
╰────────┴───────┴─────────┴────────────┴─────────┴─────────────╯
(Showing first 3 of 3 rows)
Source code in daft/functions/misc.py
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181 | def cast(expr: Expression, dtype: DataTypeLike) -> Expression:
"""Casts an expression to the given datatype if possible.
See the [casting matrix](https://docs.daft.ai/en/stable/api/datatypes/casting/) for supported casts.
Returns:
Expression: Expression with the specified new datatype
Note:
- If a string is provided, it will use the sql engine to parse the string into a data type. See the [SQL Reference](https://docs.daft.ai/en/stable/sql/datatypes/) for supported datatypes.
- a python `type` can also be provided, in which case the corresponding Daft data type will be used.
Tip: See Also
[`Expression.cast`](https://docs.daft.ai/en/stable/api/expressions/#daft.expressions.Expression.cast)
Examples:
>>> import daft
>>> df = daft.from_pydict({"float": [1.0, 2.5, None]})
>>> df = df.select(df["float"].cast(daft.DataType.int64()))
>>> df.show()
╭───────╮
│ float │
│ --- │
│ Int64 │
╞═══════╡
│ 1 │
├╌╌╌╌╌╌╌┤
│ 2 │
├╌╌╌╌╌╌╌┤
│ None │
╰───────╯
<BLANKLINE>
(Showing first 3 of 3 rows)
Example with python type and sql types:
>>> df = daft.from_pydict({"a": [1, 2, 3]})
>>> df = df.select(
... df["a"].cast(str).alias("str"),
... df["a"].cast(int).alias("int"),
... df["a"].cast(float).alias("float"),
... df["a"].cast("string").alias("sql_string"),
... df["a"].cast("int").alias("sql_int"),
... df["a"].cast("tinyint").alias("sql_tinyint"),
... )
>>> df.show()
╭────────┬───────┬─────────┬────────────┬─────────┬─────────────╮
│ str ┆ int ┆ float ┆ sql_string ┆ sql_int ┆ sql_tinyint │
│ --- ┆ --- ┆ --- ┆ --- ┆ --- ┆ --- │
│ String ┆ Int64 ┆ Float64 ┆ String ┆ Int32 ┆ Int8 │
╞════════╪═══════╪═════════╪════════════╪═════════╪═════════════╡
│ 1 ┆ 1 ┆ 1 ┆ 1 ┆ 1 ┆ 1 │
├╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ 2 ┆ 2 ┆ 2 ┆ 2 ┆ 2 ┆ 2 │
├╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ 3 ┆ 3 ┆ 3 ┆ 3 ┆ 3 ┆ 3 │
╰────────┴───────┴─────────┴────────────┴─────────┴─────────────╯
<BLANKLINE>
(Showing first 3 of 3 rows)
"""
dtype = DataType._infer(dtype)
expr = Expression._to_expression(expr)
return Expression._from_pyexpr(expr._expr.cast(dtype._dtype))
|