Counting unique items in array. (Swift)
implement the function countDistinct(numbers: [Int]) to return the number of distinct elements in the array. NSSet documentation for Swift https://developer.apple.com/documentation/foundation/nsset
func countDistinct(numbers: [Int]) -> Int {
let array:Array<Int> = numbers
let count = NSSet(array: array).count
return count
}
print(countDistinct(numbers: [20, 10, 10, 30, 20]))
As of Swift 1.2, Swift has a native Set
type. Use the Set
constructor to create a set from your array, and then the count
property will tell you how many unique items you have:
let array = [1,3,2,4,6,1,3,2]
let set = Set(array)
print(set.count) // prints "5"
For Swift 1.1 and earlier:
Turn your array into an NSSet
:
let array = [1,3,2,4,6,1,3,2]
let set = NSSet(array: array)
println(set.count) // prints "5"
You can read more about it here.
If you are interested in how many of each item you have, you can use a dictionary to count the items:
var counts = [Int:Int]()
for item in array {
counts[item] = (counts[item] ?? 0) + 1
}
print(counts) // prints "[6: 1, 2: 2, 3: 2, 1: 2, 4: 1]"
print(counts.count) // prints "5"
print("There are \(counts[1] ?? 0) ones.") // prints "There are 2 ones."
print("There are \(counts[7] ?? 0) sevens.") // prints "There are 0 sevens."
You can use NSSet to throw away duplicates:
let array:Array<Int> = [1,3,2,4,6,1,3,2]
let count = NSSet(array: array).count
println(count)
This prints:
5