计算从当前位置到 x 个对象的距离，并使用过滤器从最近到最远对它们进行排序答案

【问题标题】：Calculate the distance from current location to x objects and orders them with a filter from the nearest to the furthest计算从当前位置到 x 个对象的距离，并使用过滤器从最近到最远对它们进行排序
【发布时间】：2017-12-04 15:19:01
【问题描述】：

我创建了两个函数来计算从我的位置到 x 车的距离

func distance(from: CLLocationCoordinate2D, to: CLLocationCoordinate2D) -> CLLocationDistance {
    let from = CLLocation(latitude: from.latitude, longitude: from.longitude)
    let to = CLLocation(latitude: to.latitude, longitude: to.longitude)

    return from.distance(from: to)        
}


func selT(car:Car) {        
    guard let coordinates = car.location  else {
        return
    }
    self.destination = coordinates

    if currentLocation != nil {
        let dist = distance(from: currentLocation!, to: coordinates)
    }
}

我有一个下载汽车的功能

func getOkToDownload(download:CarsToDownload?, error : Error?) -> Void {       
    if let download = download {
        self.download = download
        if download.status == "OK" {
            if let carsDownloaded = download.cars {
                var number = numberCars / (categories?.count)!
                number = number == 0 ? 1 : number    

                let distanceC = carsDownloaded

                cars.append(contentsOf: carsDownloaded)
            }

            self.tableView?.reloadData()
        } else {
            let alert = UIAlertController.init(title: "Error", message: response.status, preferredStyle: .alert)
            alert.addAction(UIAlertAction.init(title: "Cancel", style: .cancel, handler: nil))
            alert.addAction(UIAlertAction.init(title: "Retry", style: .default, handler: { (action) in
                DispatchQueue.main.async {
                    self.showCars(true)   
                }
            }))
            self.present(viewController: alert)
        }
        showing = false
    } else {
        print("response is nil")
    }
}

其中“汽车”是var cars: [Car] = []，“下载”是CarsToDownload 类型，所以download.cars 是我要下载的汽车，现在我要做的是创建一个按顺序排列的过滤器这个函数 (getOkToDownload) 我从最近下载到最公平的汽车，为此我想我必须创建一个循环来计算 carsDownloaded 的所有距离，一旦我获得了值，用 a 对数组排序过滤，但我该怎么做？考虑到我用我展示给你的那些外部函数得到了一辆 x 车的距离值，现在我只在我的Car 类中添加了这个参数var distanceT: Float?（不知道它是否有用）

【问题讨论】：

标签： ios arrays swift for-loop

【解决方案1】：

您需要的实际计算只是两件事：根据距离过滤您的集合并按距离对该集合进行排序。我在 Playground 中扔了一些东西来说明这个过程。下面唯一真正的提升是两行代码：过滤和排序。

let mileMultiplier = 0.000621371

let home = CLLocation(latitude: 34.043017, longitude: -118.267254)
let loc1 = CLLocation(latitude: 32.689596, longitude: -117.999806)
let loc2 = CLLocation(latitude: 33.556666, longitude: -117.659812)
let loc3 = CLLocation(latitude: 34.043017, longitude: -118.467254)
let loc4 = CLLocation(latitude: 35.501326, longitude: -116.751808)
let loc5 = CLLocation(latitude: 33.986546, longitude: -117.454548)

let collection = [loc1, loc2, loc3, loc4, loc5]

func geoQueryCollection(collection: [CLLocation], radiusInMiles: Double, sorted: Bool) -> [CLLocation] {
    let results = collection.filter { $0.distance(from: home) * mileMultiplier < radiusInMiles }
    return sorted ? results.sorted { $0.distance(from: home) < $1.distance(from: home) } : results
}

let results = geoQueryCollection(collection: collection, radiusInMiles: 200, sorted: false)
results.map { print(Int($0.distance(from: home) * mileMultiplier)) }
// prints: 94, 48, 11, 132, 46

let results2 = geoQueryCollection(collection: collection, radiusInMiles: 50, sorted: true)
results2.map { print(Int($0.distance(from: home) * mileMultiplier)) }
// prints: 11, 46, 48

除了适合您需要的其他可能的改进之外，您可能希望缓存距离计算，以免重复计算，但这是起点。

【讨论】：