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Random Extensions

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Overview

Random Extensions is a library that provides functionality for pseudorandom number generation for .NET and Unity.

.NET has a built-in Random class, but it is not sufficient in terms of functionality and contains complex implementations and unnecessary abstractions due to compatibility issues.

Unity's UnityEngine.Random is a static class, making it impossible to instantiate. Additionally, it manages internal states, making it difficult to reproduce random numbers.

Random Extensions introduces IRandom as a new abstraction layer for random number generation, providing high performance implementations based on various algorithms (xoshift, xoshiro, splitmix, PCG). It also offers many useful features for handling random numbers, such as extension methods that support System.Numerics and Unity types, IWeightedCollection<T> for handling weighted random numbers, and LINQ extensions for random numbers (RandomEnumerable).

[!WARNING] Do not use this library for security purposes. If you need cryptographically secure random numbers, use System.Security.Cryptography.RandomNumberGenerator.

Installation

NuGet packages

Random Extensions requires .NET Standard 2.1 or higher. The package is available on NuGet.

.NET CLI

dotnet add package RandomEx

Package Manager

Install-Package RandomEx

Unity

You can use Random Extensions in Unity by using NugetForUnity. For more details, refer to the Unity section.

Basic Usage

You can generate random numbers using RandomEx.Shared.

using RandomExtensions;

// Get a random value between 0-9
var n = RandomEx.Shared.NextInt(0, 10);

// Get a random boolean value
var flag = RandomEx.Shared.NextBool();

You can also create an instance of IRandom initialized with a random seed using RandomEx.Create().

// Create an instance
var rand = RandomEx.Create();

// Get a random value in the range [0.0, 1.0)
var d = rand.NextDouble();

[!WARNING] Please note that RandomEx.Shared is thread-safe, but instances created with RandomEx.Create() or other classes implementing IRandom are not thread-safe.

Supported Types

Random Extensions supports more types than the standard System.Random.

var rand = RandomEx.Create();

// int
rand.NextInt();                 // [int.MinValue, int.MaxValue]
rand.NextInt(10);               // [0, 10)
rand.NextInt(10, 20);           // [10, 20)

// uint
rand.NextUInt();                // [0, uint.MaxValue]
rand.NextUInt(10);              // [0, 10)
rand.NextUInt(10, 20);          // [10, 20)

// long
rand.NextLong();                // [long.MinValue, long.MaxValue]
rand.NextLong(10);              // [0, 10)
rand.NextLong(10, 20);          // [10, 20)

// ulong
rand.NextULong();               // [0, ulong.MaxValue]
rand.NextULong(10);             // [0, 10)
rand.NextULong(10, 20);         // [10, 20)

// float
rand.NextFloat();               // [0f, 1f)
rand.NextFloat(10f);            // [0f, 10f)
rand.NextFloat(10f, 20f);       // [10f, 20f)

// double
rand.NextDouble();              // [0.0, 1.0)
rand.NextDouble(10.0);          // [0.0, 10.0)
rand.NextDouble(10.0, 20.0);    // [10.0, 20.0)
rand.NextDoubleGaussian();      // Get a random value following a Gaussian distribution with a mean of 0.0 and a standard deviation of 1.0

// byte[], Span<byte>
rand.NextBytes(buffer);          // Fill the buffer with random bytes

Additionally, by introducing the extension package, you can use methods that support types in System.Numerics and Unity. For details, see the sections on System.Numerics and Unity.

Collection Operations

Element Retrieval

You can use the GetItem() method to retrieve a random element from an array. If you want to retrieve multiple elements at once, use GetItems().

var rand = RandomEx.Create();

// Create an array of values
var values = new int[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

// Get a random element
var item = rand.GetItem(values);

// Get 5 random elements (with duplicates)
var items = rand.GetItems(values, 5);

You can also specify weights for each element. The array of weights you pass as an argument must match the number of elements in the original array.

var values = new int[] { 0, 1, 2 };
var weights = new double[] { 1.0, 5.0, 1.0 };

// Retrieve weighted random elements
var item = rand.GetItem(values, weights);
var items = rand.GetItem(values, weights, 5);

Shuffling

You can shuffle the elements of an array using the Shuffle() method.

var array = new int[] { 0, 1, 2, 3, 4, 5 };

// Shuffle the array elements
rand.Shuffle(array);

This method modifies the array itself. If you need a side-effect-free shuffle, use the following LINQ extension.

LINQ Extensions

Under the RandomExtensions.Linq namespace, there are LINQ extensions that utilize random numbers.

using System;
using System.Linq;
using RandomExtensions.Linq;

var sequence = Enumerable.Range(0, 100);

// Get a random element
var r = sequence.RandomElement();

// Shuffle the order
foreach (var item in sequence.Shuffle())
{
    Console.WriteLine(item);
}

// Create an IEnumerable<T> that yields random values in the range [0, 9] 10 times
foreach (var item in RandomEnumerable.Repeat(0, 10, 10))
{
    Console.WriteLine(item);
}

These methods can take an IRandom instance for random number generation. If not specified, RandomEx.Shared will be used.

var rand = RandomEx.Create();

// Get elements using the passed rand instance
var r = sequence.RandomElement(rand);

Weighted Collections

Under the RandomExtensions.Collections namespace, there are collections that hold weighted elements.

// Interface for a weighted collection
public interface IWeightedCollection<T> : IReadOnlyCollection<WeightedValue<T>>
{
    T GetItem<TRandom>(TRandom random) where TRandom : IRandom;
    void GetItems<TRandom>(TRandom random, Span<T> destination) where TRandom : IRandom;
}

// Struct representing a weighted element
public readonly record struct WeightedValue<T>(T Value, double Weight);

Below is a sample of using WeightedList<T> for weighted selection.

// Create a weighted list
var weightedList = new WeightedList<string>();

// Add elements with specified weights
weightedList.Add("Legendary", 0.5f);
weightedList.Add("Epic", 2.5f);
weightedList.Add("Rare", 12f);
weightedList.Add("Uncommon", 25f);
weightedList.Add("Common", 60f);

// Retrieve a weighted random element
var rarity = weightedList.GetItem();

IRandom

Random Extensions provides IRandom as an interface for random number generators. By implementing this interface, you can create custom random number generator.

public interface IRandom
{
    void InitState(uint seed);
    uint NextUInt();
    ulong NextULong();
}

IRandom Implementations

Random Extensions provides several IRandom implementations by default. Below is a list of class names and the pseudorandom number algorithms they use internally.

RandomExtensions.Algorithms

Under the RandomExtensions.Algorithms namespace, there are implementations of algorithms for generating pseudorandom numbers.

These are structs with minimal state and methods, useful in scenarios where performance is critical or state serialization is required.

Below is a sample using the XorShift32 struct to generate pseudorandom numbers.

using RandomExtensions.Algorithms;

var seed = 123456;
var xorshift = new Xorshift32(seed);

var r = xorshift.Next();

System.Numerics

RandomEx.Numerics package, available on NuGet, provides extensions that support types in System.Numerics.

.NET CLI

dotnet add package RandomEx.Numerics

Package Manager

Install-Package RandomEx.Numerics

Basic Usage

After installation, you can use the methods below.

using System.Numerics;
using RandomExtensions;
using RandomExtensions.Numerics;

var rand = RandomEx.Create();

// Vector2
rand.NextVector2();
rand.NextVector2(new Vector2(10f, 10f));
rand.NextVector2(new Vector2(10f, 10f), new Vector2(20f, 20f));
rand.NextVector2Direction();    // Get a random direction vector of length 1
rand.NextVector2InsideCircle(); // Get random point inside a unit circle

// Vector3
rand.NextVector3();
rand.NextVector3(new Vector3(10f, 10f, 10f));
rand.NextVector3(new Vector3(10f, 10f, 10f), new Vector2(20f, 20f, 20f));
rand.NextVector3Direction();    // Get a random direction vector of length 1
rand.NextVector3InsideSphere(); // Get random point inside a unit sphere

// Vector4
rand.NextVector4();
rand.NextVector4(new Vector4(10f, 10f, 10f, 10f));
rand.NextVector4(new Vector4(10f, 10f, 10f, 10f), new Vector2(20f, 20f, 20f, 20f));

// Quaternion
rand.NextQuaternionRotation();  // Get a quaternion representing a random rotation

Unity

Random Extensions is available for use in Unity and provides an extension package.

Requirements

• Unity 2021.3 or higher

Installation

1. Install NugetForUnity.

2. Open the NuGet window by selecting NuGet > Manage NuGet Packages, search for the RandomEx package, and install it.

3. Open the Package Manager window by selecting Window > Package Manager, then click on [+] > Add package from git URL and enter the following URL:

   https://github.com/AnnulusGames/RandomExtensions.git?path=src/RandomExtensions.Unity/Assets/RandomExtensions.Unity
   

Extension Methods

Under the RandomExtensions.Unity namespace, the following extension methods are available for Unity:

using UnityEngine;
using RandomExtensions;
using RandomExtensions.Unity;

var rand = RandomEx.Create();

// Vector2
rand.NextVector2();
rand.NextVector2(new Vector2(10f, 10f));
rand.NextVector2(new Vector2(10f, 10f), new Vector2(20f, 20f));
rand.NextVector2Direction();    // Get a random direction vector of length 1
rand.NextVector2InsideCircle(); // Get random point inside a unit circle

// Vector3
rand.NextVector3();
rand.NextVector3(new Vector3(10f, 10f, 10f));
rand.NextVector3(new Vector3(10f, 10f, 10f), new Vector2(20f, 20f, 20f));
rand.NextVector3Direction();    // Get a random direction vector of length 1
rand.NextVector3InsideSphere(); // Get random point inside a unit sphere

// Vector4
rand.NextVector4();
rand.NextVector4(new Vector4(10f, 10f, 10f, 10f));
rand.NextVector4(new Vector4(10f, 10f, 10f, 10f), new Vector2(20f, 20f, 20f, 20f));

// Quaternion
rand.NextQuaternionRotation();  // Get a quaternion representing a random rotation

// Color
rand.NextColor();
rand.NextColor(new Color(1f, 1f, 1f));
rand.NextColor(new Color(0f, 0f, 0f), new Color(1f, 1f, 1f));
rand.NextColorHSV(0f, 1f, 0f, 1f, 0f, 1f);          // Specify HSV range
rand.NextColorHSV(0f, 1f, 0f, 1f, 0f, 1f, 0f, 1f);  // Specify HSV and alpha range

License

This library is released under the MIT License.