Get a random unique element from an Array until all elements have been picked in Swift

Question

I have the following array:

var notebookCovers = [\"cover1\", \"cover2\", \"cover3\", \"cover4\", \"cover4\", \"cover6\", \"cover7\", \"cover8\", \"cover9\"         


        

Answer 1

If you want to create a looping solution:

let originalSet = Set(arrayLiteral: "a","b","c")
var selectableSet = originalSet

func repeatingRandomObject() -> String {
    if selectableSet.isEmpty {
        selectableSet = originalSet
    }

    return selectableSet.remove(selectableSet.randomElement()!)!
}

force unwrapping is kind of safe here, since we know that the result will never be nil. If you don't want to force unwrap:

let originalSet = Set(arrayLiteral: "a","b","c")
var selectableSet = originalSet

func repeatingRandomObject() -> String? {
    if selectableSet.isEmpty {
        selectableSet = originalSet
    }

    guard let randomElement = selectableSet.randomElement() else { return nil }
    return selectableSet.remove(randomElement)
}

Answer 2

Set is a collection type that holds unique elements. Converting your notebooks array to Set also lets you take advantage of its randomElement function

var aSet = Set(notebooks)

let element = aSet.randomElement()
aSet.remove(element)

Answer 3

It is possible with shuffle:

struct AnantShuffler<Base: MutableCollection> {

    private var collection: Base
    private var index: Base.Index

    public init?(collection: Base) {
        guard !collection.isEmpty else {
            return nil
        }
        self.collection = collection
        self.index = collection.startIndex
    }

    public mutating func next() -> Base.Iterator.Element {
        let result = collection[index]
        collection.formIndex(after: &index)
        if index == collection.endIndex {
            collection.shuffle()
            index = collection.startIndex
        }
        return result
    }
}

fileprivate extension MutableCollection {
    /// Shuffles the contents of this collection.
    mutating func shuffle() {
        let c = count
        guard c > 1 else { return }

        for (firstUnshuffled, unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) {
            let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
            let i = index(firstUnshuffled, offsetBy: d)
            swapAt(firstUnshuffled, i)
        }
    }
}

Use:

let shuffler = AnantShuffler(collection: ["c1","c2","c3"].shuffled())
shuffler?.next()

Answer 4

Copy the array. Shuffle the copy. Now just keep removing the first element until the copy is empty. When it is empty, start over.

Example:

let arr = [1,2,3,4,5]
var copy = [Int]()
for _ in 1...30 { // just to demonstrate what happens
    if copy.isEmpty { copy = arr; copy.shuffle() }
    let element = copy.removeFirst() ; print(element, terminator:" ")
}
// 4 2 3 5 1 1 5 3 2 4 4 1 2 3 5 1 4 5 2 3 3 5 4 2 1 3 2 4 5 1

Answer 5

You can try something like this,

var notebookCovers = ["cover1", "cover2", "cover3", "cover4", "cover4", "cover6", "cover7", "cover8", "cover9", "cover10"]
var tappedNotebooks: [String] = []
func tapping() {
    let notebook  =  notebookCovers[Int.random(in: 0...notebookCovers.count - 1)]
    if tappedNotebooks.contains(notebook){
        print("already exists trying again!")
        tapping()
    } else {
        tappedNotebooks.append(notebook)
        print("appended", notebook)
    }
    if tappedNotebooks == notebookCovers {
        tappedNotebooks = []
        print("cleared Tapped notebooks")
    }
}