Shuffle a slice or array

The rand.Shuffle function in package math/rand shuffles an input sequence using a given swap function.

a := []int{1, 2, 3, 4, 5, 6, 7, 8}
rand.Seed(time.Now().UnixNano())
rand.Shuffle(len(a), func(i, j int) { a[i], a[j] = a[j], a[i] })

[5 8 6 4 3 7 2 1]

Warning: Without the call to rand.Seed you will get the same sequence of pseudo­random numbers each time you run the program.

Further reading

Generate random numbers, characters and slice elements

Before Go 1.10

Use the rand.Seed and rand.Intn functions in package math/rand.

a := []int{1, 2, 3, 4, 5, 6, 7, 8}
rand.Seed(time.Now().UnixNano())
for i := len(a) - 1; i > 0; i-- { // Fisher–Yates shuffle
	j := rand.Intn(i + 1)
	a[i], a[j] = a[j], a[i]
}