Initial fileset

Author: johnsgill3

K-Means/K-Means.playground/Contents.swift

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+//
+//  K-Means.swift
+//
+//  Created by John Gill on 2/25/16.
+
+import Foundation
+
+// Need a container to easily hold 2 Dimensional Vector2Ds
+class Vector2D: CustomStringConvertible {
+    var x:Float = 0.0 // x-Coordinate of Vector2D
+    var y:Float = 0.0 // y-Coordinate of Vector2D
+    
+    init(x: Float, y: Float) {
+        self.x = x
+        self.y = y
+    }
+    
+    var description: String {
+        return "Vector2D (\(self.x), \(self.y))"
+    }
+}
+
+// Ability to use std operators on Vector2D object
+func +(left: Vector2D, right: Vector2D) -> Vector2D {
+    return Vector2D(x: left.x + right.x, y: left.y + right.y)
+}
+func +=(inout left: Vector2D, right: Vector2D) {
+    left = left + right
+}
+func /(left:Vector2D, right: Float) -> Vector2D {
+    return Vector2D(x: left.x / right, y: left.y / right)
+}
+func /=(inout left: Vector2D, right: Float) {
+    left = left / right
+}
+
+// TODO: Explain/Replace/Cleanup
+extension Array {
+    var shuffle: [Element] {
+        var elements = self
+        for index in indices {
+            let anotherIndex = Int(arc4random_uniform(UInt32(elements.count - index))) + index
+            anotherIndex != index ? swap(&elements[index], &elements[anotherIndex]) : ()
+        }
+        return elements
+    }
+    func choose(n: Int) -> [Element] {
+        return Array(shuffle.prefix(n))
+    }
+}
+
+// Calculates the Euclidean distance between two Vector2Ds
+func euclidean(v1:Vector2D, v2:Vector2D) -> Float {
+    return sqrt(pow((v1.x - v2.x), 2.0) + pow((v1.y - v2.y), 2.0))
+}
+
+// Get the INDEX of nearest Center to X
+func nearestCenter(x: Vector2D, Centers: [Vector2D]) -> Int {
+    var nearestDist = FLT_MAX
+    var minIndex:Int = 0;
+    // Calculate the distance from Vector2D X to all the centers
+    for (idx, c) in Centers.enumerate() {
+        let dist = euclidean(x, v2: c)
+        if dist < nearestDist {
+            minIndex = idx
+            nearestDist = dist
+        }
+    }
+    return minIndex
+}
+
+func kNN(numCenters: Int, convergeDist: Float, points: [Vector2D]) -> [Vector2D] {
+    var centerMoveDist:Float = 0.0
+    
+    // 1. Choose k Random Vector2Ds as the initial centers
+    var kCenters:[Vector2D] = points.choose(numCenters)
+    
+    // do following steps until convergence
+    repeat {
+        var cnts = [Float](count: numCenters, repeatedValue: 0.0)
+        var nCenters = [Vector2D](count:numCenters, repeatedValue: Vector2D(x:0, y:0))
+        // 2. Assign Vector2Ds to centers
+        //    a. Determine which center each Vector2D is closest to
+        //    b. Record how many Vector2Ds are assigned to each center
+        for p in points {
+            let c = nearestCenter(p, Centers: kCenters)
+            cnts[c]++
+            nCenters[c] += p
+        }
+        // 3. Calculate a new centers
+        for idx in 0..<numCenters {
+            nCenters[idx] /= cnts[idx]
+        }
+        // 4. Determine how far centers moved
+        centerMoveDist = 0.0
+        for idx in 0..<numCenters {
+            centerMoveDist += euclidean(kCenters[idx], v2: nCenters[idx])
+        }
+        // 5. Update centers to the newly calculated ones
+        kCenters = nCenters
+        print("Complete iteration coverge(\(centerMoveDist) <? \(convergeDist))")
+    } while(centerMoveDist > convergeDist)
+    return kCenters
+}
+var points = [Vector2D]()
+let lim = 50
+for _ in 0..<lim {
+    let x = Float(arc4random_uniform(UInt32(lim)))
+    let y = Float(arc4random_uniform(UInt32(lim)))
+    points.append(Vector2D(x: Float(x), y: y))
+}
+
+print("\nCenters")
+for c in kNN(10, convergeDist: 0.1, points: points) {
+    print(c)
+}

K-Means/K-Means.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='osx'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

K-Means/K-Means.playground/timeline.xctimeline

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+<?xml version="1.0" encoding="UTF-8"?>
+<Timeline
+   version = "3.0">
+   <TimelineItems>
+   </TimelineItems>
+</Timeline>