Collection Types

Arrays

Creating an Array by Adding Two Arrays Together

We can create a new Array with two Arrays in same types by the operator (+)

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

Accessing and Modifying an Array

We can use subcrip syntax to get or change a series values, amazing for this.

var shoppingList: [String] = ["Eggs", "Milk"]
// shoppingList has been initialized with two initial items
shoppingList[2...4] = ["Bananas", "Apples"]
// shoppingList now contains 4 items

Iterating Over an Array

If we want get the item and item index both, we can use enumerated()method, which will return a tuple including the item and item index.

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

Sets

no order, but an item only appears once, which is the difference from Array.

Hash Values for Set Types

The Sets only be able to store hashable types, which means, if we want to store some we own type, we need to make the type hashable, where we can use the Hashable Protocol to implement.

As for the String, Int, Double, Bool or something else for Swift’s basic types, which are all hashable by default.

Creating and Initializing

Unlike arrays, sets don’t have an equivalent shorthand form.

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

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

var favoriteGenres2: Set = ["Rock", "Classical", "Hip hop"]
//all values in the array literal are of the same type, Swift can infer that Set<String> is the correct type to use for the favoriteGenres variable.So no need to write the type

Iterating Over a Set

The Set type doesn’t have a defined ordering, but we can use the sorted method to make it order, this method will return the set’s elements as an array sorted by ascending.

var genre: Set = ["Jazz", "Classical", "Hip hop"]
for genre in favoriteGenres.sorted() {
    print("\(genre)")
}
// Classical
// Hip hop
// Jazz

Fundamental Set Operations

We can see the illustrations below, which show the method of fundamental set operations.

../_images/setVennDiagram_2x.png

Set Membership and Equality

let houseAnimals: Set = ["🐶", "🐱"]
let farmAnimals: Set = ["🐮", "🐔", "🐑", "🐶", "🐱"]
let cityAnimals: Set = ["🐦", "🐭"]
let cityAnimals2: Set = ["🐦", "🐭"]

houseAnimals.isSubset(of: farmAnimals)
// true
farmAnimals.isSuperset(of: houseAnimals)
// true
farmAnimals.isDisjoint(with: cityAnimals)
// true
let isEqual = (cityAnimals == cityAnimals2)
// true

Dictionaries

All is familiar enought for me, will not mention it here.

Let’s think!