Implementation:Haifengl Smile StructType

Knowledge Sources	Haifengl_Smile
Domains	Type System, Schema, Data Structures
Last Updated	2026-02-08 22:00 GMT

Overview

StructType is a record class that represents the schema of a data frame as an ordered collection of named, typed fields.

Description

StructType is a Java record implementing the DataType interface. It defines a struct data type determined by a fixed order of fields, where each field has a name, data type, and optional measurement level. The record maintains a list of StructField objects and a map from field names to ordinal indices for fast lookup. It supports field access by index or name, field mutation (set, rename, add), and provides factory methods to construct schemas from Java record/bean classes, ValueVector columns, Property arrays, and JDBC ResultSet metadata.

Usage

Use StructType when defining or inspecting the schema of a DataFrame, when reading data from databases, or when creating typed data pipelines. It is the primary schema representation in the Smile data framework.

Code Reference

Source Location

• Repository: Haifengl_Smile
• File: base/src/main/java/smile/data/type/StructType.java
• Lines: 1-371

Signature

public record StructType(List<StructField> fields, Map<String, Integer> index) implements DataType {
    // Constructors
    public StructType(List<StructField> fields);
    public StructType(StructField... fields);

    // Field access
    public int length();
    public StructField field(int i);
    public StructField field(String name);
    public StructField apply(int i);
    public StructField apply(String name);
    public int indexOf(String field);
    public String[] names();
    public DataType[] dtypes();
    public Measure[] measures();

    // Field mutation
    public void set(int i, StructField field);
    public void update(int i, StructField field);
    public void rename(String name, String newName);
    public void add(StructField field);

    // Parsing
    public List<Function<String, Object>> parser();
    public Tuple valueOf(String s);

    // DataType interface
    public String name();
    public ID id();

    // Static factory methods
    public static StructType of(ValueVector... columns);
    public static StructType of(Class<?> clazz);
    public static StructType of(Property[] props);
    public static StructType of(ResultSet rs) throws SQLException;
    public static StructType of(ResultSetMetaData meta, String dbms) throws SQLException;
}

Import

import smile.data.type.StructType;

I/O Contract

Inputs

Name	Type	Required	Description
fields	StructField[] or List<StructField>	Yes	The ordered list of struct fields defining the schema.
clazz	Class<?>	Yes (for of(Class))	A Java record or bean class to introspect.
rs	ResultSet	Yes (for of(ResultSet))	A JDBC result set to extract schema metadata from.
meta	ResultSetMetaData	Yes (for of(meta, dbms))	JDBC result set metadata.
dbms	String	Yes (for of(meta, dbms))	Database product name for type mapping.

Outputs

Name	Type	Description
StructType	StructType	The struct type representing the schema.
length()	int	The number of fields in the schema.
names()	String[]	Array of all field names.
dtypes()	DataType[]	Array of all field data types.
measures()	Measure[]	Array of all field measurement levels.
parser()	List<Function<String, Object>>	List of parsing functions for each field.

Usage Examples

Basic Usage

import smile.data.type.StructType;
import smile.data.type.StructField;
import smile.data.type.DataTypes;

// Create a schema manually
StructType schema = new StructType(
    new StructField("name", DataTypes.StringType),
    new StructField("age", DataTypes.IntType),
    new StructField("salary", DataTypes.DoubleType)
);

// Access fields
int numFields = schema.length();           // 3
StructField nameField = schema.field(0);   // name: String
int ageIndex = schema.indexOf("age");      // 1
String[] names = schema.names();           // ["name", "age", "salary"]

// Modify schema
schema.rename("salary", "income");
schema.add(new StructField("department", DataTypes.StringType));

From Java Record

import smile.data.type.StructType;

// Derive schema from a Java record
record Person(String name, int age, double height) {}
StructType schema = StructType.of(Person.class);
// Fields: name: String, age: int, height: double

Related Pages

• Implementation:Haifengl_Smile_DataType_System