Swift Set Collection: Insert and Contains

Use the set collection. Insert elements into a set, and use contains and set logic.

Set. This collection allows no duplicate elements. It uses hash codes to test for equality between elements. A set has fast logic tests.

With methods, we perform simple actions like insertion. We can test to see if an element exists. With set operations, we can see if 2 sets intersect.

First program. Here we create an empty set. We then insert() 4 strings into it. The last two strings are the same—only one is retained in the set.

Count: This returns 3, the number of elements retained in the set. The duplicate element is not counted.

Print: We use this func to display the elements present. This is a useful debugging technique.

Swift program that uses set // Create a set and add Strings to it. var animals = Set<String>() animals.insert("cat") animals.insert("bird") animals.insert("dog") animals.insert("dog") // Only unique elements are stored in the set. print(animals.count) // The second dog element is not present. print(animals) Output 3 ["bird", "cat", "dog"]

Remove, contains. We use remove() to erase an element from a set. And with contains() we see whether an element (the argument) exists. It returns true or false.

Swift program that uses remove, contains var knownIds = Set<Int>() knownIds.insert(100) knownIds.insert(200) knownIds.insert(300) // Remove this Int from the set. knownIds.remove(200) // This is contained within the set. if knownIds.contains(100) { print(true) } // Not contained. if !knownIds.contains(200) { print(false) } Output true false

For-in loop. With the for-in loop we can access all the elements in a set. This provides not indexes, but often we do not need indexes.

Swift program that uses for-in loop var languages = Set<String>() languages.insert("Swift") languages.insert("Python") languages.insert("Ruby") // Loop over all elements in the set. // ... Ordering is not maintained. for language in languages { print(language) } Output Python Ruby Swift

Intersection, subtract. This program first initializes sets with initializer syntax. This is an easier way to create a new set from known element.

Intersection: We call intersection to find the elements that are present in both sets (that intersect). A new set is returned.

Subtract: This removes elements from one set that are present in another. It modifies the first set in-place.

Swift program that uses set initializer, intersect, subtract let colors1: Set<String> = ["red", "orange", "pink"] let colors2: Set<String> = ["blue", "red", "pink"] // Intersection returns a set of the two shared Strings. // ... Red and pink are shared. let intersection = colors1.intersection(colors2) print(intersection) // Subtract removes shared values. // ... Red and pink are removed in the set. // ... The colors1 set is modified in-place. colors1.subtract(colors2) print(colors1) Output ["pink", "red"] ["orange"]

A summary. Sets have many uses in programs. They help with simple requirements, like ensuring uniqueness. More advanced things, like set operations, are less often needed.

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Swift Set Collection: Insert and Contains

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