docs/guide/python/row-format.md

title: Row Format sidebar_position: 11 id: python_row_format license: | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

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Apache Fory™ provides a random-access row format that enables reading nested fields from binary data without full deserialization.

Overview

Row format drastically reduces overhead when working with large objects where only partial data access is needed. It also supports memory-mapped files for ultra-low memory footprint.

Key Benefits:

Feature	Description
Zero-Copy Access	Read nested fields without deserializing entire object
Memory Efficiency	Memory-map large datasets directly from disk
Cross-Language	Binary format compatible between Python, Java, C++
Partial Deserialization	Deserialize only specific elements you need
High Performance	Skip unnecessary data parsing for analytics workloads

Basic Usage

import pyfory
import pyarrow as pa
from dataclasses import dataclass
from typing import List, Dict

@dataclass
class Bar:
    f1: str
    f2: List[pa.int64]

@dataclass
class Foo:
    f1: pa.int32
    f2: List[pa.int32]
    f3: Dict[str, pa.int32]
    f4: List[Bar]

# Create encoder for row format
encoder = pyfory.encoder(Foo)

# Create large dataset
foo = Foo(
    f1=10,
    f2=list(range(1_000_000)),
    f3={f"k{i}": i for i in range(1_000_000)},
    f4=[Bar(f1=f"s{i}", f2=list(range(10))) for i in range(1_000_000)]
)

# Encode to row format
binary: bytes = encoder.to_row(foo).to_bytes()

# Zero-copy access - no full deserialization needed!
foo_row = pyfory.RowData(encoder.schema, binary)
print(foo_row.f2[100000])              # Access 100,000th element directly
print(foo_row.f4[100000].f1)           # Access nested field directly
print(foo_row.f4[200000].f2[5])        # Access deeply nested field directly

Cross-Language Compatibility

Row format works seamlessly across languages. The same binary data can be accessed from Java and C++.

Java

public class Bar {
  String f1;
  List<Long> f2;
}

public class Foo {
  int f1;
  List<Integer> f2;
  Map<String, Integer> f3;
  List<Bar> f4;
}

RowEncoder<Foo> encoder = Encoders.bean(Foo.class);

// Encode to row format (cross-language compatible with Python)
BinaryRow binaryRow = encoder.toRow(foo);

// Zero-copy random access without full deserialization
BinaryArray f2Array = binaryRow.getArray(1);              // Access f2 list
BinaryArray f4Array = binaryRow.getArray(3);              // Access f4 list
BinaryRow bar10 = f4Array.getStruct(10);                  // Access 11th Bar
long value = bar10.getArray(1).getInt64(5);               // Access 6th element of bar.f2

// Partial deserialization - only deserialize what you need
RowEncoder<Bar> barEncoder = Encoders.bean(Bar.class);
Bar bar1 = barEncoder.fromRow(f4Array.getStruct(10));     // Deserialize 11th Bar only
Bar bar2 = barEncoder.fromRow(f4Array.getStruct(20));     // Deserialize 21st Bar only

C++

#include "fory/encoder/row_encoder.h"
#include "fory/row/writer.h"

struct Bar {
  std::string f1;
  std::vector<int64_t> f2;
};

FORY_FIELD_INFO(Bar, f1, f2);

struct Foo {
  int32_t f1;
  std::vector<int32_t> f2;
  std::map<std::string, int32_t> f3;
  std::vector<Bar> f4;
};

FORY_FIELD_INFO(Foo, f1, f2, f3, f4);

fory::encoder::RowEncoder<Foo> encoder;
encoder.Encode(foo);
auto row = encoder.GetWriter().ToRow();

// Zero-copy random access without full deserialization
auto f2_array = row->GetArray(1);                    // Access f2 list
auto f4_array = row->GetArray(3);                    // Access f4 list
auto bar10 = f4_array->GetStruct(10);                // Access 11th Bar
int64_t value = bar10->GetArray(1)->GetInt64(5);    // Access 6th element of bar.f2
std::string str = bar10->GetString(0);               // Access bar.f1

Installation

Row format requires Apache Arrow:

pip install pyfory[format]

When to Use Row Format

Analytics workloads: When you only need to access specific fields
Large datasets: When full deserialization is too expensive
Memory-mapped files: Working with data larger than RAM
Data pipelines: Processing data without full object reconstruction
Cross-language data sharing: When data needs to be accessed from multiple languages