Swift Learning Summary: Collection Type iosswift

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Collection Type

array
set
dictionary

collection type use are generic, the type of element is specific.
Array

With ordering.
Access by subscript.
Variable-length.

var someInts: [Int] = [] someInts.append(2) someInts = []// Empty the array

Create by class

var someDoubles = Array(repeating: 0.0, count: 3) print(someDoubles) var otherDoubles = Array(repeating: 2.5, count: 3) print(otherDoubles) var addedDoubles = someDoubles + otherDoubles// concatenate two array into one print(addedDoubles)

result:
[0.0, 0.0, 0.0]
[2.5, 2.5, 2.5]
[0.0, 0.0, 0.0, 2.5, 2.5, 2.5]

Create By Array Literal

var shoppingList = ["tomato", "milk"]

// Appending shoppingList.append("noodles") shoppingList += ["rice"] shoppingList += ["apple", "juice"]// Now the array is ["tomato", "milk", "noodles", "rice", "apples", "juice"]

Accessing

print("Count of stuff: \(shoppingList.count)")// the 'count' property is read-only.

if shoppingList.isEmpty { print("Nothing to buy.") } else { print("Have something to buy.") }

// Accessing var oneStuff = shoppingList[2]// get the "noodles"

Modifying

// Modifying shoppingList[2] = "dumplings" // Modifying a range of value shoppingList[3...5] = ["pie", "cherry", "banana"] shoppingList[3...5] = ["pie", "cherry"]// it will remove the element from 3 to 5 and just insert with two new element at position 3. //shoppingList[3...5] = ["pie", "cherry", "bread", "cookie"] the 5 is out of array's bound now, so it will trigger a run-time error. shoppingList[3...4] = ["pie", "cherry", "peach"]// it can work, just replace two element shoppingList[3] and shoppingList[4] with three new elenment. // now the array is ["tomato", "milk", "dumpings", "pie", "cherry", "peach"]// insert(_:at:) shoppingList.insert("drink", at: 0) // now the shoppingList is: ["drink", "tomato", "milk", "dumpings", "pie", "cherry", "peach"]// remove(at:) let thing = shoppingList.remove(at: 1) // The "thing" is assiged to be "tomato" // Any gaps in an array are closed when an item is removed. // So after the removing, the shoppingList is: ["drink", "milk", "dumpings", "pie", "cherry", "peach"]let last = shoppingList.removeLast() // remove the "peach"var str = shoppingList[0] str.append("s")// this will not affect the string in the shoppingList, because the String is value type, it will be copied when be passed (assigned).shoppingList[0].append("s")// this will affect the string in the shoppingList.// now the array is ["drinks", "milk", "dumpings", "pie", "cherry"]

Iterating Over an Array

for item in shoppingList { print(item) }

for (i, value) in shoppingList.enumerated() { print("Item \(i): \(value)" } // here the 'i' is a subscript of the array.

Sets

With no defined ordering.
An item only appears once.

A type must be hashable in order to be stored in a set—that is, the type must provide a way to compute a hash value for itself. if two objects’ hash values are equal, they are equally.
All of Swift’s basic types are hashable by default. (String, Int, Double,Bool, Enumeration)
Create a set

create by an Array literal

var words: Set = ["d", "i", "v", "e"] print(words) print(words.count)
- result
  ["d", "i", "e", "v"]
  4

In a shorter form```swift var words: Set = ["h", "i", "d", "e"] ```

create an instance of class Set

var letter = Set() letter.insert("H") letter.insert("e") letter.insert("a") letter.insert("r") print(letter) print(letter.count)
- result
  ["a", "r", "e", "H"]
  4

Accessing

var words: Set = ["hide", "ice", "pink", "big"] print(words.count)// it's read-only if words.isEmpty { print("words is empty.") }

Modifying

words.insert("book")var wordGet = words.remove("ice")// if words doesn't contain "ice", the removing will be invalid and the wordGet will be nil.

Iterating Over a Set

for word in words { print(word) }

Iterating in a specific order

for word in words.sorted() { print(word) }

Set Operations

intersection(_: )	create a new set with only the values common to both sets
symmetricDiffierence(_: )	create a new set with values in either set, but not both
union(_: )	create a new sew with values with all of the values in both sets
subtracting(_: )	create a new set with values not in the ‘b’ set

var a: Set = [1, 2, 5, 6] var b: Set = [1, 3, 5]var intersection = a.intersection(b)// a & b var difference = a.symmetricDifference(b) // !a & !b var union = a.union(b)// a or b var subtract = a.subtracting(b)// a - bprint(intersection) print(difference) print(union) print(subtract)

result:
[5, 1]
[2, 6, 3]
[3, 2, 1, 6, 5]
[6, 2]

Membership and Equality

==
isSubset(of: )
isSuperset(of: )
isStrictSubset(of: )
It’s a subset but not equal to.
isStrictSuperset(of: )
It’s a superset but not equal to.
isDisjoint(with: )
Two set has no values in common. They are independent with each other.

let all: Set = ["", "", "", "?♂?"] let me: Set = ["?♂?"] let emoj: Set = ["", ""] let other: Set = ["", "", "", "?♂?"] print("'me' is subset of 'all': " + String(me.isSubset(of: all))) print("'all' is superset of 'emoj': " + String(all.isSuperset(of: emoj)))print("'all' is superset of 'other': " + String(all.isSuperset(of: other))) print("'all' is subset of 'other': " + String(all.isSubset(of: other))) print("'all' is strict superset of 'other': " + String(all.isStrictSuperset(of: other))) print("'all' is strict subset of 'other': " + String(all.isStrictSuperset(of: other)))print("'other' is superset of 'all': " + String(other.isSuperset(of: all))) print("'other' is subset of 'all': " + String(other.isSubset(of: all)))
- result:
  'me' is subset of 'all': true
  'all' is superset of 'emoj': true
  'all' is superset of 'other': true
  'all' is subset of 'other': true
  'all' is strict superset of 'other': false
  'all' is strict subset of 'other': false
  'other' is superset of 'all': true
  'other' is subset of 'all': true

Dictionary

keys have same type, values have same type
with no ordering
each value is associated with a unique key
key is unique, values may be same

Swift’s Dictionary type is bridged to Foundation’s NSDictionaryclass.
The key must conform to the Hashable protocol.

Create a dictionary

by class

var pet =Dictionary() pet[11] = "dog"// adding key-value pair pet[23] = "bear"
by literal

var pet = [11: "dog", 23: bear]
properties

print(pet.count) print(pet.isEmpty)if pet[23] != nil { print(pet) }

result
2
false

Updating

pet[11] = "cat"// update the valueif let oldValue = https://www.it610.com/article/pet.updateValue("deer", forKey: 23) { // now the pet is: [11: "cat", 23: "deer"], and the oldValue is bear(optional). } else { print("oldValue is nil") }

Removing

pet[11] = nil// remove a key-value pair.pet.removeValue(forKey: 23) // remove a key-value pair.pet = [11: "cat", 23: "dog"] pet.removeAll() pet = [11: "cat", 23: "dog"] pet = [:]// clear all

Iterating Over a Dictionary

by key and value

for (key, value) in pet { print("\(key): \(value)", terminator: "\t") }
- result
  23: dog 11: cat
by key or value

var pet = [11: "cat", 23: "dog"] print() for key in pet.keys { print("\(key) ", terminator: " ") } print()for value in pet.values { print("\(value)", terminator: " ") }
- result

1123 cat dog

Get an Array from key or value

let keys = [Int](pet.keys)
let values = [String](pet.values)
get in order by calling sorted(), the object who call the sorted should implements the Comparable.

let keys = [Int](pet.keys.sorted())
the pet.sorted(using: ) need a Comparator to sort the dictionary.

Summary

Creating
- Array
  var pet: [String] = ["dog", "cat"]
- Set
  var pet: Set = ["dog", "cat"]
  var pet: Set = ["dog", "cat"]
- Dictionary
  var pet: Dictionary = Dictionary()
  var pet = [:]
  var pet: Dictionary = [23: "dog", 11: "cat"]
  var pet = [23: "dog", 11: "cat"]
Accessing and Modifying
the Array and Dictionary can access by [someKey]directly , but the Set access by insert() and remove() .
For-in
- Array
  
  for word in words {}
- Set
  
  for word in words {}
- Dictionary
  
  for (key, value) in words {}
Operation
【Swift Learning Summary: Collection Type】To generate new set, Set has some operations between two sets.