How to shuffle strings in arrays in golang?

Question

So I created a program to help me decide which game to play. Before I start my problem let me show you my code:

package main

import (
    "fmt"
    "strconv"
    "time"
)

func main() {
    isArray := [10]string{"Paladins", "Overwatch", "CS:GO", "Tanki", "Left 4 Dead", "Rocket League", "Call Of Duty : AW", "Portal", "Star Citizen", "Star Wars : Battlefront"}
    fmt.Print("0,1,2,3,4,5,6,7,8,9 := ")

    var (
        va string
        ar string
    )

    fmt.Scanln(&va)
    i, _ := strconv.Atoi(va)

    fmt.Print("You Should Play : ")
    fmt.Print(isArray[i], "\n")
    fmt.Print("[Y/N] := ")
    fmt.Scanln(&ar)

    if ar != "N" || ar != "n" {
        fmt.Print("OK")
    }

    time.Sleep(3 * time.Second)
}

So the problems start when I already know which number would trigger a game, if I use it twice. So I am trying to make the strings random, like shuffling each time I use it, how can I do that?

Possible duplicate of Randomize order of a MongoDB query in Go. — icza
– icza, Commented May 17, 2017 at 13:56

abdel · Accepted Answer · 2017-09-08 10:24:13Z

2

 package main

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

 func shuffle(src []string) []string {
         final := make([]string, len(src))
         rand.Seed(time.Now().UTC().UnixNano())
         perm := rand.Perm(len(src))

         for i, v := range perm {
                 final[v] = src[i]
         }
         return final
 }

answered Sep 8, 2017 at 10:24

abdel

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1 Comment

Mallory-Erik Over a year ago

A tidbit, UnixNano returns a UTC time value so there's actually no need for .UTC() in the seed.

denis.lobanov · Accepted Answer · 2017-05-18 17:09:22Z

0

Well, literally for your problem why not use rand.Intn() to choose a random number and print the game rather than make the user pick a number?

isArray := [10]string{"Paladins", "Overwatch", "CS:GO", "Tanki", "Left 4 Dead", "Rocket League", "Call Of Duty : AW", "Portal", "Star Citizen", "Star Wars : Battlefront"}
n := rand.Intn(9)
fmt.Printf("You Should Play : %s\n", isArray[n])

But if you want to shuffle strings in an array for the sake of it, then you can do it in place like this:

// Shuffle array in place
l := len(isArray)-1
for i := 0; i <=l; i++ {
    n := rand.Intn(l)
    // swap
    x := isArray[i]
    isArray[i] = isArray[n]
    isArray[n] = x
}

This should be O(n), though I'm not sure about the complexity of Intn. If you really want to be fancy, you could:

Create a second array (randomArray) of touples, containing a random number and element position in isArray.
Sort this array by the random number
Create a new array, copying elements of isArray, but ordered by our randomArray

edited May 18, 2017 at 17:09

answered May 17, 2017 at 14:31

denis.lobanov

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6 Comments

Dr.Topaz Over a year ago

I thought about using your first example and it doesn't work.Everytime i run the code ,it always says Left 4 Dead. PS ( i changed the value of rand.Intn(10) to rand.Intn(9) as arrays begin at 0.

denis.lobanov Over a year ago

Did you call something like rand.Seed(time.Now().UTC().UnixNano()) before rand.Intn()? Otherwise it will always generate the same number: 5

Dr.Topaz Over a year ago

whoaaa whoa whoa whoa ; i added it just now and it works :-) ,thanks man

Dr.Topaz Over a year ago

can you please explain why is it neccesary to add it before rand.Intn()

denis.lobanov Over a year ago

rand is a pseudo random number generator - given a starting number an algorithm will generate other numbers which appear random (hard to guess the next one). Because its an algorithm, if you start on the same number (seed), the next will always be the same. So you need to seed it before first use

|

Sathish Kumar Pothuri · Accepted Answer · 2018-12-09 18:53:33Z

0

package main

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

type list []string

func main() {

    s := list{
        "Tanki",
        "Left 4 Dead",
        "Rocket League",
        "Call Of Duty : AW",
    }
    s.shuffle()
    s.print()
}

func (l list) print() {
    for i, v := range l {
        fmt.Println(i, v)
    }
}

func (l list) shuffle() list {
    src := rand.NewSource(time.Now().UnixNano())
    r := rand.New(src)
    for i := range l {
        n := r.Intn(len(l) - 1)
        l[i], l[n] = l[n], l[i]
    }
    return l
}

answered Dec 9, 2018 at 18:53

Sathish Kumar Pothuri

11 bronze badge

1 Comment

Simon.S.A. Over a year ago

Welcome to stackoverflow. Please fully explain your answer. Just posting code does not help other users understand your answer.

leonardo · Accepted Answer · 2022-04-26 19:47:23Z

0

You can now use the rand.Shuffle function from the math package.

    var games = [10]string{"Paladins", "Overwatch", "CS:GO", "Tanki", "Left 4 Dead", "Rocket League", "Call Of Duty : AW", "Portal", "Star Citizen", "Star Wars : Battlefront"}

    rand.Seed(time.Now().UnixNano())
    rand.Shuffle(len(games), func(i, j int) {
        games[i], games[j] = games[j], games[i]
    })

    fmt.Println(games)

docs: https://pkg.go.dev/math/rand#Shuffle

answered Apr 26, 2022 at 19:47

leonardo

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