CODEWITHSUNDEEP
go
Nick
Nick

Reputation: 9041

How to allocate a slice of floats in Go?

I'm learning Go programming and try to test the following average function:

func average(xs []float64) float64 {
    total := 0.0
    for _, v := range xs {
        total += v
    }
    return total / float64(len(xs))
}

I tried to generate a slice of random float numbers by:

var xs []float64
for n := 0; n < 10; n++ {
    xs[n] = rand.Float64()
}

however, I got 

panic: runtime error: index out of range

Question:

  1. How to generate a slice of random number in Golang?
  2. Is expression or function call, like xs := []float64 { for ... } allowed in slice literals?

Upvotes: 3

Views: 5091

Answers (2)

Akavall
Akavall

Reputation: 86168

@hobbs answered the part about your error, but still your solution will give you the same array every time you run it because you are not passing a random seed. I would do something like this:

package main 

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

func main() {
    s := rand.NewSource(time.Now().UnixNano())
    r := rand.New(s)

    xn := make([]float64, 10)

    for n := 0; n < 10; n++ {
        xn[n] = r.Float64()
    }

    fmt.Println(xn)
}

Upvotes: 5

hobbs
hobbs

Reputation: 239781

Your method of generating the random numbers is fine, however xs is empty, and Go doesn't automatically extend slices. You could use append, however since you know the size in advance, it's most efficient to replace

var xs []float64

with

xs := make([]float64, 10)

which will give it the right size initially.

Upvotes: 9

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