How to Get a Number of Random Elements from an Array

How to get a number of random elements from an array?

Try this non-destructive (and fast) function:

function getRandom(arr, n) {
    var result = new Array(n),
        len = arr.length,
        taken = new Array(len);
    if (n > len)
        throw new RangeError("getRandom: more elements taken than available");
    while (n--) {
        var x = Math.floor(Math.random() * len);
        result[n] = arr[x in taken ? taken[x] : x];
        taken[x] = --len in taken ? taken[len] : len;
    }
    return result;
}

Get a random item from a JavaScript array

var item = items[Math.floor(Math.random()*items.length)];

How to get random elements from an array

You could shuffle the array and pick the first four.

numbers.sort( function() { return 0.5 - Math.random() } );

Now numbers[0], numbers[1]... and so on have random and unique elements.

Note that this method may not be an optimal way to shuffle an array: see Is it correct to use JavaScript Array.sort() method for shuffling? for discussion.

Getting a random value from a JavaScript array

It's a simple one-liner:

const randomElement = array[Math.floor(Math.random() * array.length)];

For example:

const months = ["January", "February", "March", "April", "May", "June", "July"];

const random = Math.floor(Math.random() * months.length);
console.log(random, months[random]);

Get random elements from array in Swift

Xcode 11 • Swift 5.1

extension Collection {
    func choose(_ n: Int) -> ArraySlice<Element> { shuffled().prefix(n) }
}

Playground testing

var alphabet = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
let shuffledAlphabet = alphabet.shuffled()  // "O", "X", "L", "D", "N", "K", "R", "E", "S", "Z", "I", "T", "H", "C", "U", "B", "W", "M", "Q", "Y", "V", "A", "G", "P", "F", "J"]
let letter = alphabet.randomElement()  // "D"
var numbers = Array(0...9)
let shuffledNumbers = numbers.shuffled()
shuffledNumbers                              // [8, 9, 3, 6, 0, 1, 4, 2, 5, 7]
numbers            // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
numbers.shuffle() // mutate it  [6, 0, 2, 3, 9, 1, 5, 7, 4, 8]
numbers            // [6, 0, 2, 3, 9, 1, 5, 7, 4, 8]
let pick3numbers = numbers.choose(3)  // [8, 9, 2]

extension RangeReplaceableCollection {
    /// Returns a new Collection shuffled
    var shuffled: Self { .init(shuffled()) }
    /// Shuffles this Collection in place
    @discardableResult
    mutating func shuffledInPlace() -> Self  {
        self = shuffled
        return self
    }
    func choose(_ n: Int) -> SubSequence { shuffled.prefix(n) }
}

var alphabetString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
let shuffledAlphabetString = alphabetString.shuffled  // "DRGXNSJLFQHPUZTBKVMYAWEICO"
let character = alphabetString.randomElement()  // "K"
alphabetString.shuffledInPlace() // mutate it  "WYQVBLGZKPFUJTHOXERADMCINS"
alphabetString            // "WYQVBLGZKPFUJTHOXERADMCINS"
let pick3Characters = alphabetString.choose(3)  // "VYA"

Picking 2 random elements from array

do NOT use loops and comparisons. Instead

shuffle the array
take first two elements

pick a random item from a javascript array

Use Math.random * the length of the array, rounded down, as an index into the array.

Like this:

var answers = [  "Hey",  "Howdy",  "Hello There",  "Wotcha",  "Alright gov'nor"]
var randomAnswer = answers[Math.floor(Math.random() * answers.length)];
console.log(randomAnswer);

How to Get a Number of Random Elements from an Array