Swift4.0でDictionaryが大幅にパワーアップした ref: https://qiita.com/hanawat/items/341a6f7843f4e19780b5

file0.swift

let touples = [("Apple", 1), ("Orange", 2), ("Grape", 3)]

// ["Grape": 3, "Orange": 2, "Apple": 1]
let dictionary = Dictionary(uniqueKeysWithValues: touples)

file1.swift

let names = ["Apple", "Orange", "Grape"]
let count = [1, 2, 3]
let ziped = zip(names, count)

// ["Grape": 3, "Orange": 2, "Apple": 1]
let dictionary = Dictionary(uniqueKeysWithValues: ziped)

file10.swift

let names = ["Apple", "Orange", "Apple", "Grape"]

var dictionary = [String: Int]()
names.forEach { dictionary[$0, default: 0] += 1 }

// ["Grape": 1, "Orange": 1, "Apple": 2]
dictionary

file11.swift

let names = ["Apple", "Grape", "Apricot", "Guava"]

var initialGroup = [Character: [String]]()
names.sorted().forEach { name in

    let character = name.characters.first ?? "#"
    var names = initialGroup[character] ?? []
    names.append(name)
    initialGroup[character] = names
}

// ["G": ["Grape", "Guava"], "A": ["Apple", "Apricot"]]
initialGroup

file12.swift

let names = ["Apple", "Grape", "Apricot", "Guava"]

// ["G": ["Grape", "Guava"], "A": ["Apple", "Apricot"]]
let initialGroup = Dictionary(grouping: names) { $0.first ?? "#" }

// [5: ["Apple", "Grape", "Guava"], 7: ["Apricot"]]
let countGroup = Dictionary(grouping: names) { $0.count }

file13.swift

var dictionary = [String: Int]()
print(dictionary.capacity) // 0

dictionary.reserveCapacity(4)
print(dictionary.capacity) // 6

dictionary.reserveCapacity(7)
print(dictionary.capacity) // 12

file2.swift

let names = ["Apple", "Apple", "Grape"]
let count = [1, 2, 3]
let ziped = zip(names, count)

// Execution was interrupted, reason: EXC_BAD_INSTRUCTION
let dictionary = Dictionary(uniqueKeysWithValues: ziped)

file3.swift

let names = ["Apple", "Apple", "Grape"]
let count = [1, 2, 3]
let ziped = zip(names, count)

// ["Grape": 3, "Apple": 3]
let merged = Dictionary(ziped, uniquingKeysWith: +)

file4.swift

let dictionary = ["Grape": 3, "Orange": 2, "Apple": 1]

// ["Grape": 6, "Orange": 2, "Apple": 4]
let merged = dictionary.merging(ziped, uniquingKeysWith: +)

file5.swift

let dictionary = ["Grape": 3, "Orange": 2, "Apple": 1]

// Swift3: [(key: "Grape", value: 3), (key: "Orange", value: 2)]
// Swift4: ["Grape": 3, "Orange": 2]
let filterd = dictionary.filter { $0.value > 1 }

file6.swift

let dictionary = ["Grape": 3, "Orange": 2, "Apple": 1]

var mapped = [String: Int]()
dictionary.forEach { touple in
    mapped[touple.key] = touple.value * 2
}

// ["Grape": 6, "Orange": 4, "Apple": 2]
mapped

file7.swift

let dictionary = ["Grape": 3, "Orange": 2, "Apple": 1]

// ["Grape": 6, "Orange": 4, "Apple": 2]
let mapped = dictionary.mapValues { $0 * 2 }

file8.swift

let dictionary = ["Grape": 3, "Orange": 2, "Apple": 1]

// 4
let potato = dictionary["Potato", default: 4]

file9.swift

let names = ["Apple", "Orange", "Apple", "Grape"]

var dictionary = [String: Int]()
names.forEach { name in

    // Binary operator '+=' cannot be applied to operands of type 'Int?' and 'Int'
    // dictionary[name] += 1

    let value = dictionary[name] ?? 0
    dictionary[name] = value + 1
}

// ["Grape": 1, "Orange": 1, "Apple": 2]
dictionary