arrays - 如何使用filter方法代替for in循环？ swift

Question

我想将 bookings 数组的每个元素的 BookingFeedback 属性分配给 arrayOfFeedBackValues。有没有比 for in 循环更短的版本？

     //long version
  let bookings = [FireBaseData]()
  var arrayOfFeedBackValues = [Double]()
       for item in bookings{
          if item.BookingFeedback != nil {
            arrayOfFeedBackValues.append(Double(item.BookingFeedback)!)
           }
       }

//attempted short version. How can I make the returned value be of type Double?
  var arrayOfFeedBackValues = bookings.filter {$0.BookingFeedback != nil}

Answer 1

您可以使用 map

arrayOfFeedBackValuesa.append(contentsOf: 
                               bookings.filter {$0.BookingFeedback != nil}
                                       .map { Double($0.BookingFeedback)! })