[Swift] 4. Collection Type

Mutability of Collections

Arrays

Array Shorthand Syntax

Creating an Empty Array

var someInts = [Int]()
print("someints is of type [Int] with \(someInts.count) items.")
// prints "someInts is of type [Int] with 0 items"

someInts.append(3)
// someInts now contains 1 value of type Int
someInts = []
// someInts is now an empty array, but is still of type [Int]

Creating an Array with a Default Value

var threeDoubles = Array(repeating: 0.0, count: 3)
// threeDoubles is of type [Double], and equals [0.0, 0.0, 0.0]

Creating an Array by Adding Two Arrays Together

var anotherThreeDoubles = Array(repeating: 2.5, count: 3)
// anotherThreeDoubles is of type [Double], and equals [2.5, 2.5, 2.5]

var sixDoubles = threeDoubles + anotherThreeDoubles
// sixDoubles is inferred as [Double], and equals [0.0, 0.0, 0.0, 2.5, 2.5, 2.5]

Creating an Array with an Array Literal

var shoppingList: [String] = ["Eggs", "Milk"]
// shoppingList has been initialized with two initial items

var shoppingList = ["Eggs", "Milk"]

Accessing and Modiftying an Array

shopping List += ["Banking Poweder"]

var firstItem = shoppingList[0]
shoppingList[0] = "Six eggs"
// index 0에 해당하는 value가 바뀜.
shoppingList[4...6] = ["bananas","apples"]
// range를 이용하여 값 변경. range의 길이와 대체 value set이 달라도 가능.

shoppingList.insert("maple syrup", at : 0)
// value를 at:index에 삽입.
shoppingList.remove(at:0)
// at:0에 해당하는 element 제거.

interating Over an Array

for item in shoppingList{
	print(item)
}

for (index,value) in shoppingList.enumerated(){
	print("Item \(index+1): \(value)")
}

Sets

Hash Values for Set Types

Creating and Initailizing an Empty Set

var letters = Set<Character>()
print("letters is of type Set<Character> width \(letters.count) items")
// Prints "letters is of type Set<Character> with 0 items.

> letters 변수의 타입은 Set<Character> 선언으로 추론된다.

letters.insert("a")
// letters now contains 1 value of type Characters
letters = []
// letters is now an empty set,but is still of type Set<Character>

Creating a Set with an Array Literal

var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]
// favoriteGenres has been initialized with three initial items

var favoriteGenres: Set = ["Rock", "Classical", "Hip hop"]

Accessing and Modifying a Set

if favoriteGenres.contains("Funk") {
    print("I get up on the good foot.")
} else {
    print("It's too funky in here.")
}
// Prints "It's too funky in here.’

Iterating Over a Set

for genre in favoriteGenres {
    print("\(genre)")
}
// Classical
// Jazz
// Hip hop

for genre in favoriteGenres.sorted() {
    print("\(genre)")
}
// Classical
// Hip hop
// Jazz

Performing Set Operations

Fundamental Set Operating

let oddDigits: Set = [1, 3, 5, 7, 9]
let evenDigits: Set = [0, 2, 4, 6, 8]
let singleDigitPrimeNumbers: Set = [2, 3, 5, 7]

oddDigits.union(evenDigits).sorted()
// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
oddDigits.intersection(evenDigits).sorted()
// []
oddDigits.subtracting(singleDigitPrimeNumbers).sorted()
// [1, 9]
oddDigits.symmetricDifference(singleDigitPrimeNumbers).sorted()
// [1, 2, 9]

Set Membership and Equality

let houseAnimals: Set = ["🐶", "🐱"]
let farmAnimals: Set = ["🐮", "🐔", "🐑", "🐶", "🐱"]
let cityAnimals: Set = ["🐦", "🐭"]

houseAnimals.isSubset(of: farmAnimals)
// true
farmAnimals.isSuperset(of: houseAnimals)
// true
farmAnimals.isDisjoint(with: cityAnimals)
// true

Dictionary

Dictionary Type Shorthand Syntax

var namesOfIntegers = [Int: String]() 
// namesOfIntegers is an empty [Int: String] dictionary
namesOfIntegers[16] = "sixteen" 
// namesOfIntegers now contains 1 key-value pair 
namesOfIntegers = [:] 
// namesOfIntegers is once again an empty dictionary of type [Int: String]

var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]
var airports = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]
//Dictionary 타입을 쓰지 않아도 type 자동 유추.

airports["LHR"] = "London" 
// the airports dictionary now contains 3 items
airports["LHR"] = "London Heathrow"
// the value for "LHR" has been changed to "London Heathrow"

if let oldValue = airports.updateValue("Dublin Airport", forKey: "DUB") { 
	print("The old value for DUB was \(oldValue).") 
} // Prints "The old value for DUB was Dublin."

if let airportName = airports["DUB"] { 
	print("The name of the airport is \(airportName).") 
} else { 
	print("That airport is not in the airports dictionary.") 
} 
// Prints "The name of the airport is Dublin Airport."

airports["APL"] = "Apple International" 
// "Apple International" is not the real airport for APL, so delete it airports["APL"] = nil 
// APL has now been removed from the dictionary

if let removedValue = airports.removeValue(forKey: "DUB"{ 
	print("The removed airport's name is \(removedValue).") 
} else { 
	print("The airports dictionary does not contain a value for DUB.") 
} 
// Prints "The removed airport's name is Dublin Airport."

for (airportCode,airportName) in airports {
	print("\(airportCode):\(airportName)")
}
// LHR : London Heathrow
// YYZ : Toronto Pearson

for airportCode in airports.keys{
	print("Airport Code : \(airportCode)")
}
// Airport code : LHR
// Airport code : YYZ

for airportName in airports.values{
	print("Airport name : \(airportName)")
}
// AirportName : London Heathrow
// AirportName : Toronto Pearson

let airportCodes = [String](airports.keys)
let airportNames = [String](airports.values)