Genetics

A lightweight and generic Genetic Algorithm, for Swift

Getting Started

To get started, you must have Swift 2.2 or later. Go to swift.org to download the latest Development snapshot

Hello World

The best way to get started is with a Hello World example, using a genetic algorithm.

The example below will take all lower case characters ["a", "b", "c", "d" ..., "z"] and attempts to produce the string "helloworld"

Using brute force, this operation as a 26^10 search space.

With Genetics, it can find the result ~80 iterations (Depending on how lucky you are).

Project Setup

First, create a project repository and create a Package.swift

$ mkdir HelloGAWorld && cd HelloGAWorld

$ touch Package.swift

Add the repoitory to your Package.swift like so:

import PackageDescription

let package = Package(name: "HelloGAWorld",
    dependencies: [
        .Package(url: "https://github.com/elliottminns/genetics", majorVersion: 0)
    ]
)

Then create a Sources directory and add the following file to it:

$ mkdir Sources

$ touch main.swift

Then, add the following code

main.swift

import Foundation

import Genetics

#if os(Linux)
    import Glibc
#else
    import Darwin
#endif

final class Algorithm {
    
    let possibleGenes = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k",
                         "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v",
                         "w", "x", "y", "z"]
    
    let algorithm = GeneticAlgorithm<String>(populationSize: 50, allowsDuplicates: true)
    
    init() {
        
        algorithm.fitnessFunction = { (chromosome: [String]) -> Int in
            
            let desired = "helloworld"
            
            let string = chromosome.joinWithSeparator("")
            
            let chars = string.characters
            
            var fitness = 0
            
            var characterSet = Set<Character>()
            
            for char in chars {
                characterSet.insert(char)
            }
            
            for char in desired.characters {
                if characterSet.contains(char) {
                    fitness += 1
                }
            }
            
            var desiredArray = desired.characters.map {
                return String($0)
            }
            
            for i in 0 ..< desiredArray.count {
                
                let desiredChar = desiredArray[i]
                
                let actualChar = chromosome[i]
                
                if desiredChar == actualChar {
                    fitness += 100
                }
            }
            
            return fitness
        }
        
        algorithm.randomMutation = { (gene: String) -> String in
            #if os(Linux)
                let newValueIndex = Int(UInt32(rand()) % UInt32(possibleGenes.count))
            #else
                let newValueIndex = Int(arc4random_uniform(UInt32(self.possibleGenes.count)))
            #endif
            
            return self.possibleGenes[newValueIndex]
        }
        
        algorithm.randomChromosome = { () -> [String] in
        
            let length = "helloworld".characters.count
            
            var chromosome: [String] = []
            
            for _ in 0 ..< length {
                chromosome.append("a")
            }
            
            return chromosome
        }
        
        algorithm.onGenerationCompleted = { generation in
            let details = self.algorithm.currentTopChromosome.joinWithSeparator("")
            print("\(generation): \(details)")
            if details == "helloworld" {
                self.algorithm.stop()
            }
        }
    }
    
    func run() {
        algorithm.runSync()
    }
}

let algorithm = Algorithm()
algorithm.run()

Then run and see the results. (Your mileage will vary)

$ swift build && .build/debug/HelloGAWorld

0: aaaaaaoaaa
1: aaaaaaoaaa
2: aaaaaaoaaa
3: aeaaxaoaaa
4: aeaaxaoaaa
5: aeaaaaoada
6: aeahxaoaad
7: tedhaaoraa
8: leaaaaoaad
9: aeahaaorad
10: leahaaorad
11: leahaaorad
12: leahaaorad
13: leahaaorad
14: leahaaorad
15: leahaaorad
16: aefhaaorld
17: aefhaaorld
18: aefhaaorld
19: aefhaaorld
20: aefhaaorld
21: aefhaaorld
22: aefhaaorld
23: aefhaaorld
24: aefhaaorld
25: wefhaaorld
26: lelhaaorld
27: veahaworld
28: veahaworld
29: veahaworld
30: veahaworld
31: veahaworld
32: veahaworld
33: veahaworld
34: veahaworld
35: veahaworld
36: welhaworld
37: welhaworld
38: welhaworld
39: welhaworld
40: welhaworld
41: welhaworld
42: welhaworld
43: uellaworld
44: uellaworld
45: uellaworld
46: lelhoworld
47: lelhoworld
48: lelhoworld
49: lelhoworld
50: lelhoworld
51: lelhoworld
52: lelhoworld
53: lelhoworld
54: velloworld
55: velloworld
56: velloworld
57: velloworld
58: velloworld
59: velloworld
60: velloworld
61: velloworld
62: velloworld
63: velloworld
64: velloworld
65: velloworld
66: velloworld
67: velloworld
68: velloworld
69: velloworld
70: velloworld
71: hellhworld
72: hellhworld
73: hellhworld
74: hellhworld
75: hellhworld
76: hellhworld
77: hellhworld
78: hellhworld
79: hellhworld
80: hellhworld
81: helloworld

Pretty neat :)

See the Wiki for more details on how to set up other projects.