Create a random number array without having a number repeat twice in a row

Question

I'm new to all of this so I hope this makes sense. I want to display random images when a button is pressed without having the same image appear twice in a row. I have found similar question on this site with answers that have helped, but I am still getting errors in my code that I do not understand.

Here is the code for my image array at the top under the class:

var imageArray:[String] = ["yes", "no", "indeed", "nope", "ofCourse", "noWay"]

Here is the code I am using for the random numbers under the button IBAction: (there are probably mistakes in this I'm not aware of, like I said earlier I am a noob)

 var currentNo: UInt32 = 0

    func randomNumber(maximum: UInt32) -> Int {

        var randomNumber: UInt32

        do {
            randomNumber = (arc4random_uniform(6))
        }while currentNo == randomNumber

        currentNo = randomNumber

        return Int(randomNumber)
    }
    var imageString:String = self.imageArray [randomNumber]

    self.iPhoneImage.image = UIImage(named: imageString)

I'm getting an error on this line:

var imageString:String = self.imageArray [randomNumber]

It says

"Cannot subscribe value of type '[String]' with an index of type '(UInt32) -> Int'

You are calling the method without parameter - var imageString:String = self.imageArray [randomNumber]. — Amit89
– Amit89, Commented Jun 27, 2015 at 5:55

Leo Dabus · Accepted Answer · 2015-06-27 08:10:55Z

1

If you don't want the random item to repeat you can remove it and append it back after the next draw as follow:

var imageArray: [String] = ["yes", "no", "indeed", "nope", "ofCourse", "noWay"]
var random: Int {
    return Int(arc4random_uniform(UInt32(imageArray.count)))
}
var lastImage = ""
var imageName: String {
    let newImage = imageArray.removeAtIndex(random)
    if lastImage != "" {
        imageArray.append(lastImage)
    }
    lastImage = newImage
    return newImage
}

Testing

println(imageName)  // "ofCourse"
println(imageName)  // "no"
println(imageName)  // "yes"
println(imageName)  // "nope"
println(imageName)  // "indeed"
println(imageName)  // "noWay" 
println(imageName)  // "ofCourse"
println(imageName)  // "noWay
println(imageName)  // "nope"
println(imageName)  // "ofCourse"
println(imageName)  // "noWay"
println(imageName)  // "yes"
println(imageName)  // "ofCourse"
println(imageName)  // "indeed"
println(imageName)  // "yes"
println(imageName)  // "nope"
println(imageName)  // "noWay"
println(imageName)  // "no"
println(imageName)  // "noWay"

edited Jun 27, 2015 at 8:10

answered Jun 27, 2015 at 6:22

Leo Dabus

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7 Comments

Dharmesh Kheni Over a year ago

yes this way it will not repeat.Great logic Leo..:)

Bill Smith Over a year ago

I ran your code and ended it with self.iPhoneImage.image = UIImage(named:imageName) But it will still occasionally use the same image twice in a row! Any idea what's going on?

Leo Dabus Over a year ago

I am pretty sure you are not running my code as it is. It removes the last element so there is no way to get repeated

Bill Smith Over a year ago

Is this right? var imageArray:[String] = ["yes", "no", "indeed", "nope", "ofCourse", "noWay"] var random:Int{ return Int(arc4random_uniform(UInt32(imageArray.count))) } var lastImage = "" var newImage = "" var imageName: String { newImage = imageArray.removeAtIndex(random) if lastImage != "" { imageArray.append(lastImage) } lastImage = newImage return newImage }

Bill Smith Over a year ago

It works perfectly! I was putting the code in the wrong spot. Thanks!

|

Dharmesh Kheni · Accepted Answer · 2015-06-27 05:56:25Z

0

This will work fine:

var imageString:String = self.imageArray[randomNumber(6)]

As you can see in your function declaration func randomNumber(maximum: UInt32) -> Int which means your function accept an argument maximum which is type of UInt32 and return Int.

But you are using your function like self.imageArray[randomNumber] where you want to access an element from imageArray with randomNumber function.

But your function accepts parameter which you doesn't assign so you can use your function this way randomNumber(6) where 6 is a max value.

And you can change your max value as per your need.

edited Jun 27, 2015 at 5:56

answered Jun 27, 2015 at 5:51

Dharmesh Kheni

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1 Comment

Bill Smith Over a year ago

Thanks! That got rid of the error and ran, but there are still Images that are appearing twice in a row. Do you know what the problem might be?

Kametrixom · Accepted Answer · 2015-09-05 10:31:37Z

With GameKit there is actually a built in random distribution that does this for you while still being uniform and pretty random:

import GameplayKit

let imageArray = ["yes", "no", "indeed", "nope", "ofCourse", "noWay"]

let randomDistribution = GKShuffledDistribution(lowestValue: 0, highestValue: imageArray.count - 1)

func randomItem() -> String {
    return imageArray[randomDistribution.nextInt()]
}

I suggest encapsulating this into its own type:

struct RandomNonRepeating<Element> {
    let values : [Element]
    let distribution : GKRandomDistribution

    init(values : [Element]) {
        self.values = values
        distribution = GKShuffledDistribution(
            lowestValue: 0, highestValue: values.count - 1)
    }

    func next() -> Element {
        return values[distribution.nextInt()]
    }
}

which can be used like this:

let x = RandomNonRepeating(values: [1, 2, 3, 4, 5])

for _ in 0...30 {
    x.next()
}

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