optimumcadence / parquet-dotnet

Apache Parquet for modern .NET

Parquet.Net

Status

Stable	Pre-release

A .NET library to read and write Apache Parquet files. Supports .NET 4.5.1, .NET Standard 1.4 and .NET Standard 1.6.

Why

Parquet library is mostly available for Java, C++ and Python, which somewhat limits .NET/C# platform in big data applications. Whereas C# is a great language we still don't have anything good in this area.

This project is aimed to fix this problem.

Index

• Supported features
• Programming guide
  • Reading Data
  • Writing Data
  • Working with DataSets
  • Supported Types
    • Working with Floating Point Data

You can track the amount of features we have implemented so far.

Related Projects

• Azure Data Lake Analytics extractor
• UWP Client for Windows 10

Getting started

Parquet.Net is redistributed as a NuGet package. All code is managed and doesn't have any native dependencies, therefore you are ready to go after referencing the package.

Reading files

In order to read a parquet file you need to open a stream first. Due to the fact that Parquet utilises file seeking extensively, the input stream must be readable and seekable. This somewhat limits the amount of streaming you can do, for instance you can't read a parquet file from a network stream as we need to jump around it, therefore you have to download it locally to disk and then open.

For instance, to read a file c:\test.parquet you woudl normally write the following code

using System.IO;
using Parquet;
using Parquet.Data;

using(Stream fs = File.OpenRead("c:\\test.parquet"))
{
	using(var reader = new ParquetReader(fs))
	{
		DataSet ds = reader.Read();
	}
}

this will read entire file in memory as a set of rows inside DataSet class.

Writing files

Parquet.Net operates on streams, therefore you need to create it first. The following example shows how to create a file on disk with two columns - id and city.

using System.IO;
using Parquet;
using Parquet.Data;

var ds = new DataSet(
	new SchemaElement<int>("id"),
	new SchemaElement<string>("city")
);

ds.Add(1, "London");
ds.Add(2, "Derby");

using(Stream fileStream = File.OpenWrite("c:\\test.parquet"))
{
	using(var writer = new ParquetWriter(fileStream))
	{
		writer.Write(ds);
	}
}

Tools

parq

Parq is a .NET runtime (written for Windows but will run elsewhere) that brings tooling for inspecting Parquet files to developers.

It is a command line utility held in a different repository, for which you can find out more by reading this guide.

License

Parquet.Net is licensed under the MIT license.

Contributing

All contributions are welcome. For details on how to start see this guide. If you are a developer who is interested in Parquet development please read this guide