Pick a random value from a Go Slice - random

Question

Situation:
I've a slice of values and need to pick up a randomly chosen value from it. Then I want to concatenate it with a fixed string. This is my code so far:
func main() {
//create the reasons slice and append reasons to it
reasons := make([]string, 0)
reasons = append(reasons,
"Locked out",
"Pipes broke",
"Food poisoning",
"Not feeling well")
message := fmt.Sprint("Gonna work from home...", pick a random reason )
}
Question:
Is there a built-in function, which can help me by doing the "pick a random reason" part?

Answer 1

Use function Intn from rand package to select a random index.
import (
"math/rand"
"time"
)
// ...
rand.Seed(time.Now().Unix()) // initialize global pseudo random generator
message := fmt.Sprint("Gonna work from home...", reasons[rand.Intn(len(reasons))])
Other solution is to use Rand object.
s := rand.NewSource(time.Now().Unix())
r := rand.New(s) // initialize local pseudorandom generator
r.Intn(len(reasons))

Answer 2

Just pick a random integer mod slice length:
rand.Seed(time.Now().Unix())
reasons := []string{
"Locked out",
"Pipes broke",
"Food poisoning",
"Not feeling well",
}
n := rand.Int() % len(reasons)
fmt.Print("Gonna work from home...", reasons[n])
Playground: http://play.golang.org/p/fEHElLJrEZ. (Note the commend about rand.Seed.)

Answer 3

Since this still shows up in Google's top results for Golang random string generation, I wanted to share what I have been working with.
Here is the solution I am using:
package main
import (
"fmt"
"strings"
"time"
)
var (
opts = strings.Split("option1,option2,option3", ",")
start = time.Now()
)
func main() {
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
}
func getRandomOpt() string {
len := len(opts)
n := uint32(0)
if len > 0 {
n = getRandomUint32() % uint32(len)
}
return opts[n]
}
func getRandomUint32() uint32 {
x := time.Now().UnixNano()
return uint32((x >> 32) ^ x)
}
And results:
option2 665ns
option1 41.406µs
option1 44.817µs
option3 47.329µs
option1 49.725µs
option3 52µs
option2 54.393µs
option2 56.798µs
option1 59.098µs
Source wise, I copied getRandomUint32() from fastrand: https://github.com/valyala/fastrand
And the solution proposed above. Performance isn't all that different, but I wanted to share results.
package main
import (
"fmt"
"math/rand"
"strings"
"time"
)
var (
opts = strings.Split("option1,option2,option3", ",")
start = time.Now()
)
func main() {
rand.Seed(start.Unix())
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
fmt.Println(getRandomOpt(), time.Since(start))
}
func getRandomOpt() string {
return opts[rand.Intn(len(opts))]
}
And results:
option3 11.865µs
option2 48.415µs
option3 52.809µs
option1 55.536µs
option3 58.191µs
option3 60.793µs
option1 63.391µs
option2 65.982µs
option2 68.601µs
These results were only run a few times locally and I grabbed what appeared to be the median result. There is certainly more work to be done in terms of iterations and whatnot, but I just wanted to share what I have.