seq.grouped(by:)

.grouped()

👉 replit

// ⭐️ seq.grouped(by:)
extension Sequence {
    public func grouped<Key>(
        by keyForValue: (Element) -> Key
    ) -> [Key: [Element]] 
    {
        return Dictionary(grouping: self, by: keyForValue)
    }
}

💈範例

👉 paiza.io

// `Dictionary` conforms to `Sequence`
let dict = [                                // Dictionary<Key, Value>
    "Sam": 79, "Joe": 5, "Mary": 18,        // Key     = String
    "Tom": 5, "Alex": 82, "Nancy": 1        // Value   = Int
]                                           // Element = (key: Key, value: Value) ⭐️

// ⭐️ seq.grouped(by:)
let grouped = dict.grouped { $0.value }     // ⭐️ grouped by element's `value`
// ⭐️ 也可寫成： dict.grouped(by: \.value)    // ⭐️ keypath as functions
/*
[
    18: [(key: "Mary" , value: 18)], 
    5 : [(key: "Tom"  , value:  5), (key: "Joe", value: 5)], 
    82: [(key: "Alex" , value: 82)], 
    1 : [(key: "Nancy", value:  1)], 
    79: [(key: "Sam"  , value: 79)]
]
*/

// ⭐️ Dictionary(grouping:by:)
let students = ["Kofi", "Abena", "Efua", "Kweku", "Akosua"]

let studentsByFirstLetter = Dictionary(
    grouping: students, 
    by: { $0.first! }
)
/// [
///   "E": ["Efua"],
///   "K": ["Kofi", "Kweku"],
///   "A": ["Abena", "Akosua"]
/// ]

📘 手冊

• SwiftUI Tutorials ⟩ Composing Complex Interfaces ⟩

  • Sec. 2: Create a Category List - Step 2.

• Swift

  • Dictionary ⟩ .init(grouping:by:)

  • Sequence ⟩ .enumerated()

👥 相關

• List

• Sequence

• ranking list

• Key Path Expressions as Functions

🗣 討論

• Swift ranking dictionary - build ranking list from scores