Random

Random numbers

Seed

Use a random seed to get a truly random number not a pseudo random number. Also, if you don’t do this, then your app will get the same value for the random calls each time.

rand.Seed(time.Now().UnixNano())

This works well locally but on the official Go playground it gives the same results each time. Maybe a better seed is needed.

Integer

rand.Int()
rand.Intn(10)

rand.Float32()
rand.Float64()

Permutations

Provide an integer and get a slice with shuffled values from zero to that value (exclusive).

x := rand.Perm(6)
// [ 0 1 3 5 4 2 ]

Get permutations of an array:

package main

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

func main() {
	rand.Seed(time.Now().UnixNano())

	s := []string{"apple", "pear", "grape", "banana", "peach", "grapefruit"}

	indexes := rand.Perm(len(s))

	for _, v := range indexes {
		fmt.Println(s[v])
	}
}

$ go run main.go

Sample output:

pear
grapefruit
banana
peach
apple
grape

apple
banana
pear
peach
grape
grapefruit

Shuffle

Shuffle pseudo-randomizes the order of elements using the default Source. n is the number of elements. Shuffle panics if n < 0. swap swaps the elements with indexes i and j.

func Shuffle(n int, swap func(i, j int))

e.g.

package main

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

func main() {
	words := strings.Fields("ink runs from the corners of my mouth")
    
	rand.Shuffle(len(words), func(i, j int) {
		words[i], words[j] = words[j], words[i]
	})
    
	fmt.Println(words)
}
// [mouth my the of runs corners from ink]