Shuffling a string in Swift

Question

I'm trying to create a word jumbler game for the iPhone using Swift. I'm relatively new to programming and Swift, but have created this game in Python previously.

Here is my pseudo-code:

//select RANDOM WORD from array

//determine the number of characters in the RANDOMLY SELECTED WORD

//randomly select a NUMBER within the boundries of the number of characters (i.e. if the word is "apple," select a number between 0 and 4)

//select the CHARACTER that corresponds to the randomly selected NUMBER

//add the CHARACTER to a new string (JUMBLE)

//remove the CHARCATER from the RANDOMLY SELECTED WORD

//Repeat until the RANDOM WORD is empty

Here is my code so far:

import UIKit

//this is my array/word bank
var words = ["Apple", "Orange", "Pear"]

//this selects a random word in the array
var selectedWord = words[Int(arc4random_uniform(UInt32(words.count)))]

//this counts the number of characters in the string
var length = (countElements(selectedWord))

//this randomly selects a position within the string
var position = Int(arc4random_uniform(UInt32(length)))

//this creates a new string consiting of the letter found in the position from the previous line of code
var subString = selectedWord[advance(selectedWord.startIndex, position)]

My issues is that I cannot figure out how to remove the selected character from the selected word. If I could, I'd simply create a loop where I repeat the process above until the original word is empty

Answer 1

Swift 5 or later

extension RangeReplaceableCollection  { 
    /// Returns a new collection containing this collection shuffled
    var shuffled: Self {
        var elements = self
        return elements.shuffleInPlace()
    }
    /// Shuffles this collection in place
    @discardableResult
    mutating func shuffleInPlace() -> Self  {
        indices.forEach {
            let subSequence = self[$0...$0]
            let index = indices.randomElement()!
            replaceSubrange($0...$0, with: self[index...index])
            replaceSubrange(index...index, with: subSequence)
        }
        return self
    }
    func choose(_ n: Int) -> SubSequence { return shuffled.prefix(n) }
}

---

let words = ["python", "jumble", "easy", "difficult", "answer", "xylophone"]

let randomWordShuffled = words.randomElement()?.shuffled ?? "" // "jmeblu"

Answer 2

You want to shuffle the contents of a String.

Easiest way is:

1. Convert the string to an array: var a = Array(selectedWord)
2. Use info from this answer to shuffle that array
3. Convert the array back into a string: let shuffledString = String(a)

So if you pick the mutating shuffle algorithm:

extension Array {
    mutating func shuffle() {
        for i in 0..<(count - 1) {
            let j = Int(arc4random_uniform(UInt32(count - i))) + i
            guard i != j else { continue}
            swap(&self[i], &self[j])
        }
    }
}

let selectedWord = "Apple"

var a = Array(selectedWord)
a.shuffle()
let shuffledWord = String(a)
// shuffledWord = “pAelp” or similar

Answer 3

func scramble(word: String) -> String {
    var chars = Array(word.characters)
    var result = ""

    while chars.count > 0 {
        let index = Int(arc4random_uniform(UInt32(chars.count - 1)))
        chars[index].writeTo(&result)
        chars.removeAtIndex(index)
    }

    return result
}

The Character struct, via word.characters in the above code, has the functionality to writeTo any OutputStreamType, including String objects. So after you write a randomly selected Character to your resulting string, simply remove it by its index and let the loop continue until there are no more characters left.

Answer 4

Here is a solution:

var myString = "abcdefg"
let shuffledString = String(Array(myString).shuffled())

Explanation:

1. Convert myString into an array of characters
2. Shuffle the Array
3. Convert the Array back into a String

Answer 5

There are many different algorithms you could use to shuffle a word, but here's one I've written in the same vein/using similar code as your current algorithm which repeatedly selects and removes a random character from your original string to add to the new string:

//this is my array/word bank
var words = ["Apple", "Orange", "Pear"]

//this selects a random word in the array
var selectedWord = words[Int(arc4random_uniform(UInt32(words.count)))]

// The string that will eventually hold the shuffled word
var shuffledWord:String = ""

// Loop until the "selectedWord" string is empty  
while countElements(selectedWord) > 0 {

    // Get the random index
    var length = countElements(selectedWord)
    var position = Int(arc4random_uniform(UInt32(length)))

    // Get the character at that random index
    var subString = selectedWord[advance(selectedWord.startIndex, position)]
    // Add the character to the shuffledWord string
    shuffledWord.append(subString)
    // Remove the character from the original selectedWord string
    selectedWord.removeAtIndex(advance(selectedWord.startIndex, position))
}

println("shuffled word: \(shuffledWord)")