91 lines
2.5 KiB
Markdown
91 lines
2.5 KiB
Markdown
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---
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title: Sets
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---
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# Sets
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Sets are a collection type that stores an **unordered list** of **distinct** values of a given type. They are useful when the order of your elements do not matter, and also when you want to ensure that an element only occurs once.
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### Initialization
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Creating an empty Set...
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```swift
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var integerSet = Set<Int>()
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```
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Using Arrays to Create Sets...
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```swift
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let posSet: Set<Int> = [0,1,2,3,4,5]
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let negSet: Set = [-1,-2,-3,-4,-5]
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```
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### Set Modification
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Insert and Remove an element from a set.
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```swift
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integerSet.insert(10312018) //insert the integer "10312018" into the set
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integerSet.remove(10312018) //remove the integer "10312018" from the set
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```
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### Set Operations
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There are four fundamental set operations that can be performed on sets: union, intersection, subtraction, and symmetric difference
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_Note_: The **sorted()** method used in the proceeding code, returns an array of the the elements of the set sorted in ascending order. It is primarily used in the below code for clarity.
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**_Union_:** combines the elements of two sets
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```swift
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integerSet = integerSet.union(posSet) // performs a union operation that returns a new set
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integerSet.formUnion(negSet) // performs a union operation that modifies the current set
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integerSet.sorted() // [-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5]
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```
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**_Intersection_:** forms a set from only the common values of two sets
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```swift
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let oddSet: Set = [1,3,5,9]
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let _ = integerSet.intersection(oddSet).sorted(); // [1,3,5]
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```
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**_Symmetric Difference_:** forms a set from the values that are not common in both sets.
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```swift
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let inbetweenSet: Set<Int> = [-4,-3,-2,-1,0,1,2,3,4]
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let _ = integerSet.symmetricDifference(inbetweenSet).sorted() // [-5,5]
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```
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**_Subtraction_:** : forms a set with values not in the specified set.
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```swift
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integerSet.subtract(negSet)
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integerSet.sorted() // [0, 1, 2, 3, 4, 5]
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```
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### Iterating Over a Set
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You can iterate over a set by using a for-in loop...
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```swift
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var showSet = "";
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for item in integerSet {
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showSet += "\(item) "
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}
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print(showSet)
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```
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The output for the above code is going to be along the lines of "1 5 4 3 0 2"... which of course is not in order. To iterate over a set in an orderly fashion use the sorted() method...
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```swift
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showSet = "";
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for item in integerSet.sorted() {
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showSet += "\(item) "
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}
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print(showSet)
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```
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Output: "0 1 2 3 4 5"
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#### More Information:
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* [The Swift Programming Language](https://docs.swift.org/swift-book/LanguageGuide/CollectionTypes.html#ID484)
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