How to increase or decrease the probability of an item of an array being picked-CodePudding

Lets say I have an array of numbers like this:

// Create Array Of Numbers
let numbers = ["1","2","3","4","5"]

If I want to print a random number from the array, I can do something like:

pickedNumber = Int.random(in: 0...numbers.count - 1)

The above line will return a random value from my array.

What I would like to do is, set a probability for each value in the array. For example:

- Chance of 1 being picked at 10%
- Chance of 2 being picked at 20%
- Chance of 3 being picked at 30%
- Chance of 4 being picked at 35%
- Chance of 5 being picked at 5%

What's the best approach for this? Any guidance or advice would be appreciated. This problem I am facing is in swiftUI.

CodePudding user response：

more of a mathematical question than an UI question, but nevertheless:

let probs = [
    1 : 10,
    2 : 20,
    3 : 30,
    4 : 35,
    5 : 5
]

func randomWithProbability(distribution: [Int : Int]) -> Int {
    
    var distributionArray: [Int] = []
    distribution.forEach { (key: Int, value: Int) in
        let new = Array(repeating: key, count: value)
        distributionArray.append(contentsOf: new)
    }
    let r = Int.random(in: 0..<distributionArray.count)
    return distributionArray[r]
    
}

and to prove it:

struct ContentView: View {
    
    private var results: [Int]
    
    init() {
        results = [0,0,0,0,0]
        for _ in 0..<1000 {
            let i = randomWithProbability(distribution: probs)
            results[i-1]  = 1
        }
    }
    
    var body: some View {
        
        VStack(alignment: .leading) {
            ForEach(results.indices) { i in
                HStack {
                    Text("\(i)")
                    Color.blue
                        .frame(width: CGFloat(results[i]), height: 40)
                }
            }
        }
    }
}

CodePudding user response：

Add 1 10 times to your array, 2 20 times, and so on. Your Array will have 100 elements so you will control the probability for each element.

If your values are always going to be multiples of 5% you can use an array of 20 elements and add a proportional number of values.