Find closest location between user's coordinates and coordinates array

Question

I want to create a function that takes as parameters:

1. An array filled of coordinates
2. The current user location

And return the closest location between the user's location and the array locations.

Here are my locations:

let coord1 = CLLocation(latitude: 52.45678, longitude: 13.98765)
let coord2 = CLLocation(latitude: 52.12345, longitude: 13.54321)
let coord3 = CLLocation(latitude: 48.771896, longitude: 2.270748000000026)

User location function:

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    var userLocation:CLLocation = locations[0]
    let long = userLocation.coordinate.longitude;
    let lat = userLocation.coordinate.latitude;

    let coordinates = [ coord1, coord2, coord3]

    userLocation = CLLocation(latitude: lat, longitude: long)

    print("my location: \(userLocation)")
    closestLocation(locations: coordinates, closestToLocation: userLocation)
}

Coordinates comparison function

    func closestLocation(locations: [CLLocation], closestToLocation location: CLLocation) -> CLLocation? {

    if let closestLocation: CLLocation = locations.min(by: { userLocation.distance(from: $0) < userLocation.distance(from: $1) }) {

        let distanceMeters = userLocation.distance(from: closestLocation)
        let distanceKM = distanceMeters / 1000

        print("closest location: \(closestLocation), distance: \(distanceKM)")
        return closestLocation
    } else {
        print("coordinates is empty")
        return nil
    }

}

It actually doesn't working and my closestLocation function is always returning a huge distance between the two "closest locations".

Input parameters

closestLocation(locations: coordinates, closestToLocation: userLocation)

Edit

Result when I print closestLocation and distanceKM:

closest location: <+48.77189600,+2.27074800> +/- 0.00m (speed -1.00 mps / course -1.00) @ 14/01/2017 00:16:04 heure normale d’Europe centrale, distance: 5409.0

As you can see, the distance (in km) is very huge while these locations are the same city.

Answer 1

You can use Array.min(by: ) to find the minimum element according to a sorting criteria (distance in your case):

func closestLocation(locations: [CLLocation], closestToLocation location: CLLocation) -> CLLocation? {
    if let closestLocation = locations.min(by: { location.distance(from: $0) < location.distance(from: $1) }) {
        print("closest location: \(closestLocation), distance: \(location.distance(from: closestLocation))")
        return closestLocation
    } else {
        print("coordinates is empty")
        return nil
    }
}

// We know the answer is coord3 and the distance is 0    
closestLocation(locations: [coord1, coord2, coord3], closestToLocation: coord3)