Swift Collections - Dictionary

SwiftCollectionsDictionary.swift

//DICTIONARIES


//1. Create

//IMMUTABLE (size and contents cannot be changed)
let immutableResponseMessages = [200: "OK",
                                 403: "Access forbidden",
                                 404: "File not found",
                                 500: "Internal server error"]

//responseMessages[200] = nil //forbidden

//MUTABLE
//Initialiser Syntax
//var emptyDict1: Dictionary<Int, String> = Dictionary<Int, String>()
//var emptyDict2: Dictionary<Int, String> = [Int: String]()
//var emptyDict3 = [Int: String?]()

//Dictionary Literals Syntax
//var emptyDict4: [Int: String] = [:]

var additionalResponseMessages = [301: "Moved permanently",
                                  200: "Working"]

var mutableResponseMessages = immutableResponseMessages//make mutable copy


//2. Check

let elements = immutableResponseMessages.count
let isEmpty = immutableResponseMessages.isEmpty

//2. Access
let response = immutableResponseMessages[200]

//enumerate with sorted keys
for key in immutableResponseMessages.keys.sorted() {
    print(immutableResponseMessages[key]!)
}

//enumerate both keys and values in random order
for (key, value) in immutableResponseMessages {
    print("Response for: \(key) is '\(value)'")
}

//enumerate only values (sorted)
for value in immutableResponseMessages.values.sorted() {
    print(value)
}


//3. Mutate

//UPDATE
//mutableResponseMessages[200] = "Very OK"
//let previousValue = mutableResponseMessages.updateValue("Very Very OK", forKey: 200)
//print(mutableResponseMessages[200]!)

//REMOVE
//mutableResponseMessages[200] = nil
//let previousValue = mutableResponseMessages.removeValue(forKey: 200)

//MERGE
let merged = immutableResponseMessages.merging(additionalResponseMessages) { (first, second) -> String in
    return first
}
print(merged)


//4. Transform

let errorMessages = merged.filter { (key, value) -> Bool in
    return key >= 300
}
//print(errorMessages)

//Dictionary is a Sequence, so it has a map method which produces array.
let values = merged.map { $0.value.uppercased() }
//print(values)

//We can still keep dictionary structure using mapValues method.
let mappedDictionary = errorMessages.mapValues { $0.uppercased() }
print(mappedDictionary)