Generate random Strings without a shuffle and repetition of previous ones? - arrays

Question

My code already generates a random String of an array when I press a button, but sometimes a String gets repeated. What do I have to do so that the String "Mango" only gets called again when all the other Strings where already called without using a shuffle, I want to call one String at a time?
Example: "Mango", "Kiwi", "Banana", "Pineapple", "Melon", "Mango", "Kiwi",.....
Here is my code:
var array = ["Mango", "Banana", "Apple","Kiwi", "Melon", "Pineapple"]
let fruits = Int(arc4random_uniform(UInt32(array.count)))
print(array[fruits])

Answer 1

In order to avoid repetitions you need to keep track of which fruits have previously been seen. There are several ways to do that an all of the proposed solutions do it in one way or another.
For your specific use case, you will need this tracking to be retained outside of the code executed by the button (in your view controller for example).
Here is a generalized structure that could help with this:
(you can define it inside the view controller if this is a one-time thing or outside of it if you intend to reuse the mechanism elsewhere)
struct RandomItems
{
var items : [String]
var seen = 0
init(_ items:[String])
{ self.items = items }
mutating func next() -> String
{
let index = Int(arc4random_uniform(UInt32(items.count - seen)))
let item = items.remove(at:index)
items.append(item)
seen = (seen + 1) % items.count
return item
}
}
To use it, you would declare a variable (in your VC) that will keep track of your fruits:
var fruits = RandomItems(["Mango", "Banana", "Apple","Kiwi", "Melon", "Pineapple"])
And in the button's code use that variable (fruits) to print a non-repeating fruit name at each execution
func buttonPressed() // <- use your function here
{
print( fruits.next() )
}

Answer 2

You need to implement some logic. It's quite easy if you think harder. Run this in your Playground, or if you fully understand this block of code, you can do this in your project already.
var array = ["Mango", "Banana", "Apple","Kiwi", "Melon", "Pineapple"]
var selectedIndices = [Int]()
for _ in 1...20 {
let randomFruitIndex = Int(arc4random_uniform(UInt32(array.count)))
// Print only if not yet printed once
if !selectedIndices.contains(randomFruitIndex) {
print(array[randomFruitIndex])
selectedIndices.append(randomFruitIndex)
}
// Reset
if selectedIndices.count == array.count {
print("----- CLEARING SELECTED INDICES----")
selectedIndices.removeAll()
}
}
So as you can see, we are adding each generated random number (in your case, it's the fruits variable.) into an array of Int. Then if the number of selectedIndices is equal to the count of the array of fruits, clear all the stored selectedIndices.
OUTPUT:
Pineapple
Melon
Mango
Kiwi
Banana
Apple
----- CLEARING SELECTED INDICES----
Mango
Melon

Answer 3

This is an adaption from the accepted answer of the linked topic in my comment:
var source = ["Mango", "Banana", "Apple","Kiwi", "Melon", "Pineapple"]
var usedElements = [String]()
func choosePseudoRandomElement() -> String {
if source.count == 0 {
source = usedElements
usedElements = []
}
let randomIndex = Int(arc4random_uniform(UInt32(source.count)))
let randomItem = source[randomIndex]
usedElements.append(randomItem)
source.remove(at: randomIndex)
return randomItem
}
for _ in 1...18 {
print("Item: \(choosePseudoRandomElement())")
}
One potential issue with this solution is that it may happen, that the last element of one complete iteration also occurs as the first element of the second iteration. You can handle that case by comparing the randomly chosen item with the item which was chosen before (use a while loop until the items doesn't match anymore).
Also, this does remove elements from the source array. If you do not want that, create a copy of the source array.