json_filter.swift

json_filter.swift

let persons: [[String: Any]] = [["name": "Carl Saxon", "city": "New York, NY", "age": 44],
                                      ["name": "Travis Downing", "city": "El Segundo, CA", "age": 34],
                                      ["name": "Liz Parker", "city": "San Francisco, CA", "age": 32],
                                      ["name": "John Newden", "city": "New Jersey, NY", "age": 21],
                                      ["name": "Hector Simons", "city": "San Diego, CA", "age": 37],
                                      ["name": "Brian Neo", "age": 27]] //注意这家伙没有 city 键值
func infoFromState( state: String, persons: [[String: Any]])
    -> Int {
        // 先进行 flatMap 后进行 filter 筛选
        // $0["city"] 是一个可选值，对于那些没有 city 属性的项返回 nil
        // componentsSeparatedByString 处理键值，例如 "New York, NY"
        // 最后返回的 ["New York","NY"]，last 取到最后的 NY
        let x = persons.flatMap( {
            guard let x = $0["city"] else {return nil}
            return  (x as! String).components(separatedBy:", ").last })
            .filter({$0 == state
            }
        )
        
        return x.count
}
let count = infoFromState(state: "CA", persons: persons)