如何在新数组中捕获过滤值答案

【问题标题】：How to capture filtered values in new array如何在新数组中捕获过滤值
【发布时间】：2017-09-04 15:59:52
【问题描述】：

我正在实现一个“在我周围搜索”功能，类似于可以在谷歌地图上找到的功能。我有一个名为“locations”的数组，其中填充了如下值：

mapPoints(Borough: "Manhattan", Neighborhood: "Battery Park City", Latitude: 40.7117, Longitude: -74.0158),

函数“myPlaces()”是实现“搜索我”功能的地方。当按下按钮时，“myPlaces()”被触发。里面是 func myPlaces(){

        for location in locations{


            let userLocation = mapView.userLocation
            let userLat = userLocation?.coordinate.latitude
            let userLong = userLocation?.coordinate.longitude

            let coordinateOne = CLLocation(latitude: userLat!, longitude: userLong!)
            let coordinateTwo = CLLocation(latitude: location.latitude, longitude: location.longitude)

            let distanceFromPoints = coordinateOne.distance(from: coordinateTwo)
            let convertToMiles = distanceFromPoints*0.00062137
            if convertToMiles >= 2 {
                print("It's greater than set amount")
            } else{
                let annotation = MGLPointAnnotation()
                filteredLocations = locations
                print("amount to come out", filteredLocations.count)
                annotation.title = location.Neighborhood
                annotation.coordinate = CLLocationCoordinate2D(latitude: location.latitude, longitude: location.longitude)
                mapView.addAnnotation(annotation)
                mapView.setCenter((mapView.userLocation?.coordinate)!, zoomLevel: 11, animated: true)

                }
            }
    animateOut()
}

现在的问题是我需要取小于 2 的值，并将它们放在一个名为“filteredLocationsmapPoints”的新数组中，这样我就可以在我的其余代码中访问它们

【问题讨论】：

标签： ios arrays swift sorting filter

【解决方案1】：

你在寻找这样的东西吗？

let filteredLocations = locations.filter {
   (location) in 
   let userLocation = mapView.userLocation
   let userLat = userLocation?.coordinate.latitude
   let userLong = userLocation?.coordinate.longitude

   let coordinateOne = CLLocation(latitude: userLat!, longitude: userLong!)
   let coordinateTwo = CLLocation(latitude: location.latitude, longitude: location.longitude)

   let distanceFromPoints = coordinateOne.distance(from: coordinateTwo)
   let convertToMiles = distanceFromPoints*0.00062137
   return convertToMiles < 2
}

使用过滤器会将您的数组构建为单个功能操作，而不是命令式循环方法。这很有效，因为您已经有了识别所需逻辑的逻辑。

使用 map 语句获取您的注释，这会遍历一个集合以产生另一个东西。

let annotations = filteredLocations.map {
   (location) in
   let annotation = MGLPointAnnotation()
   annotation.title = location.Neighborhood
   annotation.coordinate = // etc
   return annotation
}

然后，您可以使用 for 语句简单地将注释添加到地图中（或者，如果它符合您的喜好，我猜在映射函数中，但由于这是“副作用”而不起作用）

for annotation in annotations { 
   mapView.addAnnotation(annotation) 
}

mapView.setCenter((mapView.userLocation?.coordinate)!, zoomLevel: 11, animated: true)

这还有一个好处是设置地图视图的中心一次，而不是在 for 循环中！

【讨论】：

感谢您的回复！我如何能够添加filteredLocations中的注释点[原始函数中“else”语句之后的部分]
已更新注释！

【解决方案2】：

在类的顶部创建一个新数组，将其命名为 filtersLocationsmapPoints

var filteredLocationsmapPoints = [CGFloat]()

现在在你的 for 循环中添加小于 2 的那些

for location in locations{


        let userLocation = mapView.userLocation
        let userLat = userLocation?.coordinate.latitude
        let userLong = userLocation?.coordinate.longitude

        let coordinateOne = CLLocation(latitude: userLat!, longitude: userLong!)
        let coordinateTwo = CLLocation(latitude: location.latitude, longitude: location.longitude)

        let distanceFromPoints = coordinateOne.distance(from: coordinateTwo)
        let convertToMiles = distanceFromPoints*0.00062137
        if convertToMiles >= 2 {
            print("It's greater than set amount")
        } else{
            // here you append the values which are less than 2
            filteredLocationsmapPoints.append(convertToMiles)

            let annotation = MGLPointAnnotation()
            filteredLocations = locations
            print("amount to come out", filteredLocations.count)
            annotation.title = location.Neighborhood
            annotation.coordinate = CLLocationCoordinate2D(latitude: location.latitude, longitude: location.longitude)
            mapView.addAnnotation(annotation)
            mapView.setCenter((mapView.userLocation?.coordinate)!, zoomLevel: 11, animated: true)

            }
        }
animateOut()

}

【讨论】：