[Swift] Dictionary

Dictionary

- Element = Unique Key + Value

- Unordered Collection

※ Dictionary Literal

//var dictFromLiteral = ["key 1": "value 1", "key 2": "value 2"]
//var dictFromLiteral = [1: "value 1", 2: "value 2"]
var dictFromLiteral = ["1": 1, "2": 2]

//var dictFromLiteral = [:]
dictFromLiteral = [:]

※ Dictionary Type

let words1: Dictionary = ["A": "Apple", "B": "Banana", "C": "City"]
let words2: [String: String] = ["A": "Apple", "B": "Banana", "C": "City"]
let words3 = ["A": "Apple", "B": "Banana", "C": "City"]

※ Number of Element

var words = ["A": "Apple", "B": "Banana", "C": "City"]
let countOfWords = words.count

if !words.isEmpty {
    print("\(countOfWords) element(s)")
} else {
    print("empty dictionary")
}

※ Retrieve an Element

if let aValue = words["A"] {
    print(aValue)
} else {
    print("Not found")
}

if let zValue = words["Z"] {
    print(zValue)
} else {
    print("Not found")
}

print(words.keys)
print(words.values)

let keys = Array(words.keys)
let values = Array(words.values)

※ Searching

//var words = ["A": "Apple", "B": "Banana", "C": "City"]

if words.contains(where: { (key, value) -> Bool in
    return key == "A"
    }){
    print("contains A key.")
}

if words.contains(where: { (dict) -> Bool in
    return dict.value.lowercased() == "City".lowercased()
}) {
    print("contains City value.")
}

if words.contains(where: { $0.1.lowercased() == "City".lowercased() }) {
    print("contains City value.")
}

let filteringResult = words.filter { (key, value) -> Bool in
    return value.lowercased().contains("a")
}


for (key, value) in filteringResult {
    print("\(key) - \(value)")
}

※ Add a New Element

words = ["A": "A"]

words["A"]    // Key -> Unique

words["A"] = "Apple"
words

words["B"] = "Banana"
words

words["B"] = "Blue"
words

※ Change an Existing Element

words = [:]
words["A"] = "Apple111"
words

words = [:]

if let oldValue = words.updateValue("Apple", forKey: "A") {
    print("\(oldValue) => \(words["A"]!)")
} else {
    print("+ \(words["A"]!)")
}

words

if let oldValue = words.updateValue("Apricot", forKey: "A") {
    print("\(oldValue) => \(words["A"]!)")
} else {
    print("+ \(words["A"]!)")
}

※ Remove an Element

//words = ["A": "Apple", "B": "Banana", "C": "City"]
words = ["A": "Apple", "B": "Banana", "C": "City", "Z": "Zoo"]
words["Z"] = "ZZZ"
words["Z"] = nil
words

words["EE"] = nil
words

words = ["A": "Apple", "B": "Banana", "C": "City",
         "D": "Drama", "E": "Earth", "F": "Fuel"]

if let removedValue = words.removeValue(forKey: "D") {
    print("\(removedValue) removed!")
}

words

words.removeAll()

※ Enumerating an Dictionary

let dict = ["A": "Apple", "B": "Banana", "C": "City"]

for (key, value) in dict {
    print("\(key): \(value)")
}

for (key, _) in dict {
    print(key)
}

for (_, value) in dict {
    print(value)
}

var d = [String: [String]]()
//d["d"] = "A"
d["d"] = ["A"]

let _ = [String: [String: Int]]()