Implementation:Eventual Inc Daft Expression Cast

Knowledge Sources	Daft Daft Docs
Domains	Data_Engineering, Data_Transformation
Last Updated	2026-02-08 00:00 GMT

Overview

Concrete tool for converting expression values between data types provided by the Daft library.

Description

The cast method on Daft's Expression class converts column values from their current data type to a specified target type. It delegates to daft.functions.cast internally. The cast is applied element-wise and supports conversions between numeric types, string to numeric parsing, timestamp to date extraction, and other compatible type pairs.

Usage

Use .cast() on any Daft expression when you need to convert its data type. This is a method on Expression instances and requires importing DataType from Daft to specify the target type.

Code Reference

Source Location

• Repository: Daft
• File: daft/expressions/expressions.py
• Lines: L490-498

Signature

def cast(self, dtype: DataTypeLike) -> Expression

Import

from daft import col, DataType

# Cast a column to a target type
col("x").cast(DataType.int64())
col("y").cast(DataType.string())

I/O Contract

Inputs

Name	Type	Required	Description
dtype	DataTypeLike	Yes	The target data type to cast the expression to (e.g., DataType.int64(), DataType.string())

Outputs

Name	Type	Description
return	Expression	A new Expression with values cast to the specified data type

Usage Examples

Basic Usage

import daft
from daft import col, DataType

# Create DataFrame with string numbers
df = daft.from_pydict({"x": ["1", "2", "3"]})

# Cast string column to integer
df = df.with_column("x_int", col("x").cast(DataType.int64()))
df.show()
# Output:
# x: ["1", "2", "3"]
# x_int: [1, 2, 3]

Float to Integer

import daft
from daft import col, DataType

df = daft.from_pydict({"price": [19.99, 24.50, 9.99]})

# Cast float to integer (truncates decimal places)
df = df.with_column("price_rounded", col("price").cast(DataType.int64()))
df.show()
# Output:
# price: [19.99, 24.50, 9.99]
# price_rounded: [19, 24, 9]

Related Pages

Implements Principle

• Principle:Eventual_Inc_Daft_Type_Casting

Requires Environment

• Environment:Eventual_Inc_Daft_Python_PyArrow_Core