Collection Types

Question 1

What are Swift’s three primary collection types?

Answer 1

Arrays, sets, and dictionaries.

Question 2

What do collection types collect?

Answer 2

Values.

Question 3

What is an array?

Answer 3

An ordered collection of values.

Question 4

What is a set?

Answer 4

An unordered collection of unique values.

Question 5

What is a dictionary?

Answer 5

Unordered collections of key-value associations.

Question 6

If assigned to a variable, are collections mutable or immutable?

Answer 6

Mutable, it’s size and contents can be changed.

Question 7

If assigned to a constant, are collections mutable or immutable?

Answer 7

Immutable, it’s size and contents cannot be changed.

Question 8

An array stores values of the _____ type in an _______ list.

Answer 8

Same, ordered.

Question 9

In an array, can the same value appear multiple times at different positions?

Answer 9

Yes.

Question 10

How do you write the type of array?

Answer 10

Array where element is the type of value the array is allowed to store.

Question 11

How do you create an empty array of a certain type using initializer syntax? (Give an example using someInts as the var)

Answer 11

var someInts = [Int]()
     someInts = [] (if there is already context)

Question 12

Create an array with a default value (3 doubles of equal value)

Answer 12

var threeDoubles = Double

Question 13

Create an array by adding two arrays together.

Answer 13

Add name of first array variable and second array variable together. EX: var sixDoubles = threeDoubles + anotherThreeDoubles

Question 14

What is an array literal?

Answer 14

A shorthand way to write one or more values as an array collection. EX: var shoppingList: [String] = [“Eggs”, “Milk”]

Question 15

You can access and modify an array by using what kind of syntax?

Answer 15

Subscript. EX: var firstItem = shoppingList[0]

Question 16

Name two ways to add an item to the end of an array.

Answer 16

Use the method .append(_:)

nameOfArray += [“Item to add”]

Question 17

The first item in an array has a value of what?

Answer 17

Zero.

Question 18

Use subscript syntax to change the first item in the shoppingList array to “Six eggs”.

Answer 18

shoppingList[0] = “Six eggs”

Question 19

How do you replace a range of values in an array?

Answer 19

shoppingList{4…6] = [“Bananas”, “Apples”]

Question 20

Can you use subscript syntax to append a new item to the end of an array?

Answer 20

No.

Question 21

How would you insert “Maple Syrup” to value zero in the shoppingList array?

Answer 21

shoppingList.insert(“Maple Syrup”, atIndex: 0)

Question 22

How would you remove “Maple Syrup” from value zero in the shoppingList array?

Answer 22

let mapleSyrup = shoppingList.removeAtIndex(0)

Question 23

How would you remove the last item in the shoppingList array (“apples”)?

Answer 23

let apples = shoppingList.removeLast()

Question 24

How would you iterate over the entire set of values in the shoppingList array?

Answer 24

for item in shoppingList {
 print(item)
 }
 // Six eggs
 // Milk
 // Flour
 // Baking Powder
// Bananas

Question 25

How would you enumerate each item of the shoppingList array?

Answer 25

``` for (index, value) in shoppingList.enumerate() { print("Item \(index + 1): \(value)") } // Item 1: Six eggs // Item 2: Milk // Item 3: Flour // Item 4: Baking Powder // Item 5: Bananas ```

Question 26

In sets, do items appear once or more than once?

Answer 26

Once.

Question 27

What is a hash value?

Answer 27

An Int value that is the same for all objects that compare equally, such that if a = b, it follows that a.hashValue == b.hashValue.

Question 28

Are all of Swift’s basic types (String, Int, Double, Bool) hashable by default?

Answer 28

Yes.

Question 29

How is a type of a set written?

Answer 29

Set where Element is the type that the set is allowed to store.

Question 30

Create an empty set of a certain type (Character) using initializer syntax for the variable “letters”.

Answer 30

var letters = Set() OR letters = []

Question 31

Can you initialize a set with an array literal as a shorthand way to write one or more values as a set collection?

Answer 31

Yes.

Question 32

How would you create a set (“favoriteGenres”) consisting of Rock, Classical, and Hip Hop with an array literal?

Answer 32

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

Question 33

Can a set type be inferred from a literal array alone?

Answer 33

No. The type must be explicitly declared.

Question 34

How do you access and modify a set?

Answer 34

Through its methods and properties.

Question 35

How would you check to see if favoriteGenres includes Funk?

Answer 35

if favoriteGenres.contains(“Funk”)

Question 36

How do you iterate over the values in a set?

Answer 36

With a for-in loop. ``` for genre in favoriteGenres { print("\(genre)") } // Classical // Jazz // Hip hop ```

Question 37

How would you iterate over the values of a set in a specific order?

Answer 37

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

Question 38

Name four fundamental set operations.

Answer 38

Intersect, exclusiveOr, union, subtract.

Question 39

What method creates a new set with only the values common to both sets?

Answer 39

.intersect(_:)

Question 40

What method creates a new set with values in either set, but not both?

Answer 40

.exclusiveOr(_:)

Question 41

What method creates a new set with all of the values in both sets?

Answer 41

.union(_:)

Question 42

What method creates a new set with values not in the specified set?

Answer 42

.subtract(_:)

Question 43

What is a superset?

Answer 43

A set that contains all the elements of another set and of itself.

Question 44

What is a subset?

Answer 44

A set that’s elements are also contained in another set.

Question 45

What are disjoint sets?

Answer 45

Two sets that do share no common elements.

Question 46

What method determines whether all of the values of a set are contained in the specified set?

Answer 46

.isSubsetOf(_:)

Question 47

What method determines whether a set contains all of the values in a specified set?

Answer 47

.isSupersetOf(_:)

Question 48

What methods determine whether a set is a subset or superset, but not equal to, a specified set?

Answer 48

.isStrictSubsetOf(_:) | .isStrictSupersetOf(_:)

Question 49

When do you use a dictionary?

Answer 49

When you need to look u values based on their identified, in much the same way that a real-world dictionary is used to look up the definition of a particular word.

Question 50

Create an empty Dictionary (namesOfIntegers) of a String type by using initializer syntax.

Answer 50

var namesOfIntegers = [Int: String]()

Question 51

Can Swift infer set type information?

Answer 51

Yes, it can.

Question 52

Create a namesOfIntegers empty dictionary with an empty dictionary literal.

Answer 52

namesOfIntegers = [:]

Question 53

Create a dictionary to store the names of international airports with a key standing for the airport’s three-letter code and the value as the airport name.

Answer 53

var airports: [String: String] = [“YYZ”: “Toronto Pearson”, “DUB”: “Dublin”]

Question 54

What dictionary method sets or updates the value for a particular key?

Answer 54

.updateValue(_:forKey:)

Question 55

The .updateValue(_:forKey:) method returns what of the dictionary’s value type?

Answer 55

An optional value (e.g., String? or “optional String” with the optional string containing the old value for that key if one existed before.)

Question 56

You can remove a key-value pair from a dictionary by assigning what value for that key?

Answer 56

nil

Question 57

What method removes a key-value pair from a dictionary?

Answer 57

.removeValueForKey(_:)

Question 58

How can you iterate over the key-value pairs in a dictionary?

Answer 58

With a for-in loop. for (airportCode, airportName) in airports { ``` print("\(airportCode): \(airportName)") } // YYZ: Toronto Pearson // LHR: London Heathrow ```

Question 59

How can you retrieve an utterable collection of dictionary’s keys or values?

Answer 59

By accessing its keys and values properties. for airportCode in airports.keys { print("Airport code: \(airportCode)") } ``` // Airport code: YYZ // Airport code: LHR ``` for airportName in airports.values { print("Airport name: \(airportName)") } ``` // Airport name: Toronto Pearson // Airport name: London Heathrow ```

Question 60

If you need to use a dictionary’s keys or values with an API that takes an array instance, what should you do?

Answer 60

Initialize a new array with the keys or values property. ``` let airportCodes = [String](airports.keys) // airportCodes is ["YYZ", "LHR"] ``` ``` let airportNames = [String](airports.values) // airportNames is ["Toronto Pearson", "London Heathrow"] ```

Question 61

What method should you use to iterate over the keys or values of a dictionary in a specific order?

Answer 61

.sort()