NEW: Master Swift design patterns with my latest book! >>

How to generate fair random numbers using GKShuffledDistribution

Written by Paul Hudson    @twostraws

A so-called “fair” random number generator is one that generates each of its possible values in equal amounts and with an even distribution. For example, if you were generating numbers between 1 and 4, you might get 4, 2, 1, 3, but you would never get 4 4 1 4.

GameplayKit has support for fair random number generation using GKShuffledDistribution. First, add an import for the GameplayKit framework:

import GameplayKit

Second, create an instance of GKShuffledDistribution, telling it the lowest and highest values it can generate:

let distribution = GKShuffledDistribution(lowestValue: 1, highestValue: 8)

Finally, call nextInt() on it as needed to generate numbers. You should get all numbers between 1 and 8 at least once before you see any repeated.

Available from iOS 9.0 – see Hacking with Swift tutorial 35

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Get the ultimate experience

The Swift Power Pack includes my first six books for one low price, helping you jumpstart a new career in iOS development – check it out!

Click here to visit the Hacking with Swift store >>