Swift Sets

In Swift, a set is used to store unique elements of the same data type.

Syntax

var setName = Set<Type>()

var setName: Set = [value1, value2, ...]

Type refers to the data type of the values to be stored in the set.

To create a set populated with values, use the Set keyword before the assignment operator. The values of the set must be contained within brackets [] and separated with commas ,.

Empty Sets

An empty set is a set that contains no values inside.

var team = Set<String>()

print(team)
// Output: []

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Iterating Over a Set

A for-in loop can be used to iterate over each item in a set.

var recipe: Set = ["Chocolate chips", "Eggs", "Flour", "Sugar"]

for ingredient in recipe {
  print("Include \(ingredient) in the recipe.")
}

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.isEmpty Property

Use the built-in property .isEmpty to check if a set has no values contained in it.

var emptySet = Set<String>()

print(emptySet.isEmpty)  // Prints: true

var populatedSet: Set = [1, 2, 3]

print(populatedSet.isEmpty) // Prints: false

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.count Property

The property .count returns the number of elements contained within a set.

var band: Set = ["Guitar", "Bass", "Drums", "Vocals"]

print("There are \(band.count) players in the band.")
// Output: There are 4 players in the band.

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Methods

There are many set manipulation methods available in the Swift Standard Library, including generic Collection-based methods. Some of these include testing the contents of sets (e.g. .contains() and .isEmpty) while others can modify or manipulate the set entirely (e.g., .map(), .reduce(), and .sorted()). There is also a list of methods applicable to a pair of sets (e.g., .intersection() or .subtracting()).

Below are some methods available for sets: