Having Trouble with Random Numbers in Swift - swift

Question

I am trying to generate random background colors to display to a user when they press a button on the screen. I have an immutable array of UIColor items and I have made a mutable copy to manipulate. When a random color is generated, that color is then returned and removed from the mutable copy of the array to prevent consecutive showings of the same color until all colors have been shown. This is supposed to happen until the array's count is 0, and then it recreates the array to repeat the process. However, when I get down to the array having between 2 and 0 items, the loop seems to turn into an infinite loop. What logic am I missing in my code (playground file)?
var currentColorIndexNumber = 0
var newColorIndexNumber = 0
let colorsArray = [
UIColor(red: 90/255.0, green: 187/255.0, blue: 181/255.0, alpha: 1.0), //teal color
UIColor(red: 222/255.0, green: 171/255.0, blue: 66/255.0, alpha: 1.0), //yellow color
UIColor(red: 223/255.0, green: 86/255.0, blue: 94/255.0, alpha: 1.0), //red color
UIColor(red: 239/255.0, green: 130/255.0, blue: 100/255.0, alpha: 1.0), //orange color
UIColor(red: 77/255.0, green: 75/255.0, blue: 82/255.0, alpha: 1.0), //dark color
UIColor(red: 105/255.0, green: 94/255.0, blue: 133/255.0, alpha: 1.0), //purple color
UIColor(red: 85/255.0, green: 176/255.0, blue: 112/255.0, alpha: 1.0), //green color
]
var mutableColorsArray: [AnyObject] = colorsArray
func randomNumber() -> Int {
// avoid repeating random integers
while currentColorIndexNumber == newColorIndexNumber {
var unsignedArrayCount = UInt32(mutableColorsArray.count)
var unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
newColorIndexNumber = Int(unsignedRandomNumber)
}
currentColorIndexNumber = newColorIndexNumber
return newColorIndexNumber
}
func randomColor() -> UIColor {
var randomIndex = randomNumber()
var randomColor = mutableColorsArray[randomIndex] as UIColor
mutableColorsArray.removeAtIndex(randomIndex)
if mutableColorsArray.count == 0 {
mutableColorsArray = colorsArray
}
return randomColor
}

Answer 1

Try shuffling instead. Something along these lines:
var colorsArray = ["red","green","blue","yellow","purple"]
var currentColorIndexNumber = colorsArray.count
func shuffle<T>(inout array: Array<T>) -> Void {
for index in 0..<colorsArray.count {
let swapLocation = index + Int(arc4random_uniform(UInt32(colorsArray.count - index)))
if index != swapLocation {
swap(&array[swapLocation], &array[index])
}
}
}
func randomColor() -> String {
// shuffle first time through, then every time the list is exhausted
if currentColorIndexNumber >= colorsArray.count - 1 {
// shuffle, but guarantee first color after shuffling
// is not the same as last color from previous round
do {
shuffle(&colorsArray)
} while colorsArray[0] == lastColor
currentColorIndexNumber = -1
lastColor = colorsArray[colorsArray.count-1]
}
currentColorIndexNumber += 1
return colorsArray[currentColorIndexNumber]
}
for i in (5*colorsArray.count) {
print("\(randomColor()) ")
if i % colorsArray.count == 0 {
println()
}
}

Answer 2

I have had good results with
func randomObject(array: [AnyObject]) -> AnyObject {
return array[Int(arc4random_uniform(UInt32(array.count)))]
}
To enumerate all of the elements in random order, just use a shuffle function as the one below, use the elements of the shuffled array in order and re-shuffle the array once it is exhausted.
func shuffleArray<T>(array: Array<T>) -> Array<T> {
for var i = array.count - 1; i > 0; i-- {
var j = Int(arc4random_uniform(UInt32(i-1)))
swap(&array[i], &array[j])
}
return array
}