对 Swift 中嵌套自定义对象的值求和

Question

我正在尝试将在 Swift 中的某些自定义对象中找到的值相加。我有以下代码在 Playground 中工作：

//Custom Object
class EntryPack: NSObject{
  var date: String!
  var duration: Double!
  var customValues:[CustomValuePack] = [] //Nested array of objects declared below
}

//Another object to nest in the above
class CustomValuePack: NSObject{
  var name:String!
  var value: Double!
}

//Instantiate nested objects
let cv1 = CustomValuePack()
  cv1.name = "Day"
  cv1.value = 1.2
let cv2 = CustomValuePack()
  cv2.name = "Day"
  cv2.value = 1.3
let cv3 = CustomValuePack()
  cv2.name = "Night"
  cv2.value = 2.2

//Instantiate parent objects
let entry1 = EntryPack()
  entry1.date = "bingo"
  entry1.duration = 1.1

  entry1.customValues = [cv1, cv2]

let entry2 = EntryPack()
  entry2.date = "bingo"
  entry2.duration = 2.2

let entry3 = EntryPack()
  entry3.date = "dang"
  entry3.duration = 3.0

//Throw it all together into an array
var package = [entry1, entry2, entry3]

//Predicate for some filtering
let predicate = NSPredicate(format:"date = %@", "bingo")
let results = (package as NSArray).filteredArrayUsingPredicate(predicate) as! [EntryPack]

//Sum all the parent object durations
let sum = results.reduce(0.0) { [=11=] + .duration }

print(sum) // = 3.3

但现在我想为每个 CustomValuePack 添加 value，其中 name 是 "Day"。

我不知道如何对嵌套的对象数组进行类似的归约。我试过这样的东西，但它会产生语法错误：

let sum2 = results.reduce(0.0) { [=12=].customValues + .customValues.value } //Error

如何对嵌套对象数组中的值求和？ 我最终也想应用 NSPredicate 来按 name = Day 进行过滤，但我还没那么远。

Answer 1

给定entries定义如下

let entries = [entry1, entry2, entry3]

您可以提取名称 == "Day" 的 CustomValues 并用此代码对值字段求和

let sum = entries
    .flatMap { [=11=].customValues }
    .filter { [=11=].name == "Day" }
    .map { [=11=].value }
    .reduce(0, combine: +)

改进

您正在使用 Swift，但由于某种原因，您的代码中仍有很多 Objective-C。

这就是我重构您的代码的方式

struct EntryPack {
    let date: String
    let duration: Double
    let customValues:[CustomValuePack]
}

struct CustomValuePack {
    let name:String
    let value: Double
}

let cv1 = CustomValuePack(name: "Day", value: 1.2)
let cv2 = CustomValuePack(name: "Day", value: 1.3)
let cv3 = CustomValuePack(name: "Night", value: 2.2)

let entry1 = EntryPack(date: "bingo", duration: 1.1, customValues: [cv1, cv2])
let entry2 = EntryPack(date: "bingo", duration: 2.2, customValues: [])
let entry3 = EntryPack(date: "dang", duration: 3.0, customValues: [])

Please note that now EntryPack and CustomValuePack are structs which are value types.

对 Swift 中嵌套自定义对象的值求和

Sum the Values of Nested Custom Objects in Swift

nspredicate

swift

改进