Weighted randomisation in swift?

Question

Created Dec ’20

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I have a function that calculates a random genotype. At the moment all genes are equally likely. In reality, some genes are more likely than others. How can I change my function to be more realistic? I have attached some example percentages (they don't add up yet)

Code Block     func calculateGenotype() {
    //grey 10% of "G" appearing, 90% chance of "g" appearing
    greGenotype = ["G", "g"][Int.random(in:0...1)]+["G", "g"][Int.random(in:0...1)]
    //single tobiano 5% of "To" appearing, 95% of "to" appearing
    tobGenotype = ["To", "to"][Int.random(in:0...1)]+["To", "to"][Int.random(in:0...1)]
    }

Answered by OOPer in 650983022

I do not know if such functionality is included in the Standard Library or any other frameworks of Apple's, but you can write it by yourself.

Code Block func weightedRandom<Value>(weightedValues: (value: Value, weight: Double)...) -> Value {
    let rnd = Double.random(in: 0.0...100.0)
    var accWeight = 0.0
    for (value, weight) in weightedValues {
        accWeight += weight
        //print(rnd, accWeight)
        if rnd <= accWeight {
            return value
        }
    }
    //If the sum of weights is less the 100%, the last value is returned
    return weightedValues.last!.value
}
let greGenotype: String
let tobGenotype: String
greGenotype =
    weightedRandom(weightedValues: ("G", 10), ("g", 90)) +
    weightedRandom(weightedValues: ("G", 10), ("g", 90))
tobGenotype =
    weightedRandom(weightedValues: ("To", 5), ("to", 95)) +
    weightedRandom(weightedValues: ("To", 5), ("to", 95))
print(greGenotype, tobGenotype)

(Seems 10 to 90 or 5 to 95 is too small for debugging.)

Boost

Answer 1

OOPer OP

Dec ’20

Accepted Answer

I do not know if such functionality is included in the Standard Library or any other frameworks of Apple's, but you can write it by yourself.

Code Block func weightedRandom<Value>(weightedValues: (value: Value, weight: Double)...) -> Value {
    let rnd = Double.random(in: 0.0...100.0)
    var accWeight = 0.0
    for (value, weight) in weightedValues {
        accWeight += weight
        //print(rnd, accWeight)
        if rnd <= accWeight {
            return value
        }
    }
    //If the sum of weights is less the 100%, the last value is returned
    return weightedValues.last!.value
}
let greGenotype: String
let tobGenotype: String
greGenotype =
    weightedRandom(weightedValues: ("G", 10), ("g", 90)) +
    weightedRandom(weightedValues: ("G", 10), ("g", 90))
tobGenotype =
    weightedRandom(weightedValues: ("To", 5), ("to", 95)) +
    weightedRandom(weightedValues: ("To", 5), ("to", 95))
print(greGenotype, tobGenotype)

(Seems 10 to 90 or 5 to 95 is too small for debugging.)

0

Answer 2

imey OP

Dec ’20

Thanks, this works :)

0