Generate random float64 numbers in specific range using Golang

Question

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func genRandNums(min, max float64) []float64 {
    var randNums []float64
    s := rand.NewSource(time.Now().Unix())
    r := rand.New(s)
    for x := 0; x < 10; x++ {
        // generate random float in range of min and max inclusive, append
        // to randNums and return randNums
    }
    return randNums
}

func main() {
    nums := genRandNums(1.10, 101.98)
    fmt.Println(nums)
}

I have tried searching online on how to accomplish this, but I only found out how to generate random integers in a range. Is there any way I can generate random floats in a range using Go stdlib?

Answer 1

Simply use rand.Float64() to get a random number in the range of [0..1), and you can map (project) that to the range of [min..max) like this:

r := min + rand.Float64() * (max - min)

And don't create a new rand.Rand and / or rand.Source in your function, just create a global one or use the global one of the math/rand package. But don't forget to initialize it once.

Here's an example function doing that:

func randFloats(min, max float64, n int) []float64 {
    res := make([]float64, n)
    for i := range res {
        res[i] = min + rand.Float64() * (max - min)
    }
    return res
}

Using it:

func main() {
    rand.Seed(time.Now().UnixNano())
    fmt.Println(randFloats(1.10, 101.98, 5))
}

Output (try it on the Go Playground):

[51.43243344285539 51.92791316776663 45.04754409242326 28.77642913403846
    58.21730813384373]

Some notes:

• The code on the Go playground will always give the same random numbers (time is fixed, so most likely the Seed will always be the same, also output is cached)
• The above solution is safe for concurrent use, because it uses rand.Float64() which uses the global rand which is safe. Should you create your own rand.Rand using a source obtained by rand.NewSource(), that would not be safe and neither the randFloats() using it.