結構參數 - 陣列

Question

這裏有一個簡單的代碼：

struct Car { 
    var model: String 
    var producer: String 
    var year: Int 
} 

func AverageYear(years : [Int]) -> Int { 
    var x : Int = 0 
    for i in 0..<years.count { 
     x += years[i] 
    } 
    return x/years.count 
} 

var list = [Car(model: "C400", producer: "Mercedes-benz", year: 2014), 
      Car(model: "GLE450", producer: "Mercedes-benz", year: 2016)] 

print(AverageYear([list[0].year, list[1].year])) 

我怎麼能代替AverageYear([list[0].year, list[1].year]) - 無需枚舉所有的元素？喜歡的東西AverageYear([list.year])

Answer 1

您可以使用地圖從汽車的給定的數組一樣，建設年數組：

var list = [Car(model: "C400", producer: "Mercedes-benz", year: 2014), 
      Car(model: "GLE450", producer: "Mercedes-benz", year: 2016)] 

let years = list.map { $0.year } 
print(AverageYear(years)) 

Answer 2

減少使得它在一個單一的線上工作：

struct Car { 
    var model: String 
    var producer: String 
    var year: Int 
} 

var list = [Car(model: "C400", producer: "Mercedes-benz", year: 2014), 
      Car(model: "GLE450", producer: "Mercedes-benz", year: 2016)] 

// slice the array to get the elements you want 
let slice = list[0...1] 

// sum every car.year in the slice and divide by the count 
let averageYear: Int = slice.reduce(0){ $0 + $1.year }/slice.count 

print(averageYear) // -> 2015 

公告我使用list[0...1]，這意味着「元素0到1，包括」。它返回原始數組的一部分。如果我有10個元素，我可以做list[5...8]，它會給我一個元素分片5,6,7,8。