SmoothedLocationPlayground2.swift

import CoreLocation

extension CLLocation {
    public static func +(lhs: CLLocation, rhs: CLLocation) -> CLLocation {
        let summedLat  = lhs.coordinate.latitude  + rhs.coordinate.latitude
        let summedLong = lhs.coordinate.longitude + rhs.coordinate.longitude
        return CLLocation(latitude: summedLat, longitude: summedLong)
    }
    
    public static func /(lhs: CLLocation, rhs: Double) -> CLLocation {
        let dividedLat  = lhs.coordinate.latitude  / rhs
        let dividedLong = lhs.coordinate.longitude / rhs
        return CLLocation(latitude: dividedLat, longitude: dividedLong)
    }
}

extension Collection {
    /// Splits a collection into its first element and a SubSequence of the rest of its elements.
    func split() -> (head: Element, tail: SubSequence)? {
        guard let first = first else {
            return nil
        }
        
        return (first, dropFirst())
    }
    
    /// A simpler form of reduce. E.g., `[1, 2, 3].reduce(+) == 6`
    func reduce(_ nextPartialResult: (Element, Element) throws -> Element) rethrows -> Element? {
        guard let (head, tail) = split() else {
            return nil
        }
        
        return try tail.reduce(head, nextPartialResult)
    }
}

let coordinates = [
    (438.0, 236.0),
    (439.0, 237.0),
    (440.0, 238.0),
    (450.0, 250.0),
    (442.0, 240.0),
    (444.0, 242.0)
]

// initialize the locations and sort them by distance to the origin
let locations = coordinates
    .map(CLLocation.init)
    .sorted { (loc1, loc2) -> Bool in
        loc1.coordinate.latitude * loc1.coordinate.longitude < loc2.coordinate.latitude * loc2.coordinate.longitude
    }

// discard the bottom quartile, which probably contains outliers
let realisticLocations = locations.prefix(3 * locations.count / 4)

let averageLocation = realisticLocations.reduce(+)! / Double(realisticLocations.count)
print(averageLocation.coordinate)