Iterating over a Set in Swift

In Swift, there are two main ways to iterate through a set. The first approach is to use a for-in loop, and the second one is to use the forEach() method. You can also use some high-order functions that work with collections, such as map(), reduce(), or filter() to perform various operations on a given set.

Using a for-in loop

Example:

let mySet = Set(["Sling", "Academy", "Swift", "iOS"])

for element in mySet {
    print(element)
}

Output:

Sling
Academy
Swift
iOS

The order of the elements is not guaranteed because sets are unordered collections.

Using the forEach() method

Example:

let numbers: Set<Int> = [1, 2, 3, 4, 5]
numbers.forEach { element in
    print(element)
}

Output:

3
2
1
4
5

You can also write the code in a more concise style like this:

let numbers: Set<Int> = [1, 2, 3, 4, 5]
numbers.forEach{ print($0)}

Once again, the order of the elements in the output is not guaranteed.

Iterating over a sorted set

Suppose you want to print the elements of a set in a consistent order then you can use the sorted() method to create an array of sorted elements and then use either a for-in loop or a forEach() method on that array.

Example:

import Foundation

// create a set of words
var words: Set<String> = ["slingacademy.com", "swift", "ios", "programming"]

// create an array of sorted elements from the set
var sortedwords = words.sorted()

// iterate over the sorted array using a for-in loop
for word in sortedwords {
    print(word)
}

// iterate over the sorted array using the forEach() method
sortedwords.forEach { word in
    print(word)
}

Using high-order functions with a a set

Example:

// create a set of numbers
var numbers: Set<Int> = [1, 2, 3, 4, 5]

// use map() to create a new set with each element squared
var squaredNumbers = numbers.map { $0 * $0 }
print(squaredNumbers) // [16, 1, 9, 25, 4]

// use reduce() to create a single value by adding all the elements
var sum = numbers.reduce(0, +)
print(sum) // 15

// use filter() to create a new set with only the even elements
var evenNumbers = numbers.filter { $0 % 2 == 0 }
print(evenNumbers) // [2, 4]