Swift 将项作为字典值添加到数组中

我正试图找出在

Swift

中向

数组添加值的最佳方法，该数组是
字典中的
值。我想建立一个按联系人名字的第一个字母排序的联系人字典。例如[A:[Aaron，Adam，etc…]，B:[Brian，Brittany，etc…]，]

我发现这个函数：

updateValue（\uuuquokey:）

并尝试在循环中使用它：

for contact in self.contacts.sorted() {
    self.contactDictionary.updateValue([contact], forKey: String(describing: contact.characters.first))           
}

但是当我尝试使用它时，它用一个新的数组替换了现有的数组。我知道我可以手动检查字典中的键是否存在，如果存在，则检索数组，然后附加新值，否则添加新的键/值对，但我不确定Swift是否提供了一种更简单/更好的方法

任何见解都将不胜感激
 您可以使用
reduce（into:）
方法（Swift4），如下所示：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
    // make sure there is at least one letter in your string else return
    guard let first = element.first else { return }
    // create a string with that initial
    let initial = String(first)
    // initialize an array with one element or add another element to the existing value
    result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]

let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)


如果使用Swift3或更早版本，则需要在闭包内创建可变结果字典：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
    var result = result
    guard let first = element.first else { return result }
    let initial = String(first)
    result[initial] = (result[initial] ?? []) + [element]
    return result 
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]


请注意，结果没有排序。字典是无序的集合。如果需要对字典进行排序并返回（键、值）元组数组，可以使用按键排序，如下所示：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
    // make sure there is at least one letter in your string else return
    guard let first = element.first else { return }
    // create a string with that initial
    let initial = String(first)
    // initialize an array with one element or add another element to the existing value
    result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]

let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)

let sorted=dictionary.sorted{$0.key<$1.key}
打印（已排序）

[（键：“A”，值：[“亚伦”，“亚当]），（键：“B”，值：[“布莱恩”，“布列塔尼]）]\n

您可以使用
reduce（into:）
方法（Swift4），如下所示：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
    // make sure there is at least one letter in your string else return
    guard let first = element.first else { return }
    // create a string with that initial
    let initial = String(first)
    // initialize an array with one element or add another element to the existing value
    result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]

let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)


如果使用Swift3或更早版本，则需要在闭包内创建可变结果字典：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
    var result = result
    guard let first = element.first else { return result }
    let initial = String(first)
    result[initial] = (result[initial] ?? []) + [element]
    return result 
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]


请注意，结果没有排序。字典是无序的集合。如果需要对字典进行排序并返回（键、值）元组数组，可以使用按键排序，如下所示：

let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
    // make sure there is at least one letter in your string else return
    guard let first = element.first else { return }
    // create a string with that initial
    let initial = String(first)
    // initialize an array with one element or add another element to the existing value
    result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary)   // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]

let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)

let sorted=dictionary.sorted{$0.key<$1.key}
打印（已排序）

[（键：“A”，值：[“亚伦”，“亚当]），（键：“B”，值：[“布莱恩”，“布列塔尼]）]\n

Swift 4的新字典初始值设定器可以为您完成所有功能：

let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0])  } 
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)

Swift 4的新字典初始值设定器可以为您完成所有功能：

let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0])  } 
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)

是的，但您不需要再访问characters属性。确实，旧习惯很难改变。这要求所有元素至少有一个Character注意，characters属性已被弃用，以防崩溃。您可以使用flatMap
let dict=[Character:[String]]（contacts.flatMap{$0.first==nil？nil:（$0.first！，[$0]），uniquingKeysWith:+）
是的，但您不需要再访问characters属性。事实上，旧习惯很难改变。这要求所有元素至少有一个Character注意，characters属性已被弃用，以防崩溃。您可以使用flatMap
let dict=[Character:[String]]（contacts.flatMap{$0.first==nil？nil:（$0.first！，[$0]），uniquingKeysWith:+）