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

Question

var array = ["one", "two", "three", "four", "five"];
var item = array[Math.floor(Math.random()*array.length)];

The code above selects a random item from the array. However, how could I get it to select 3 random elements from the array at once, rather than only one.

Rather than only selecting three for example, it should be something like two five one.

first make an array to store selected items `var items=[]` then you can fill it in a loop, and as you select your item, also splice it from `array`, or you can use nested while loops, one checking if there's <3 elements in your items array, one checks if new item is already in it — d3vi4nt, Jan 01 '17 at 22:10
Try adapting this answer: http://stackoverflow.com/a/3943985/145346 — Mottie, Jan 01 '17 at 22:10

score 8 · Answer 1 · answered Jan 01 '17 at 22:16

8

You could use a dummy array for counting and a copy of the array and splice the random items without shuffling the array.

var array = ["one", "two", "three", "four", "five"],
    result = array.slice(0, 3).map(function () { 
        return this.splice(Math.floor(Math.random() * this.length), 1)[0];
    }, array.slice());

console.log(result);

answered Jan 01 '17 at 22:16

Nina Scholz

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Always nice to see your solutions :) – Dekel Jan 01 '17 at 22:21

score 3 · Answer 2 · edited May 23 '17 at 12:01

You can shuffle() the array and then get the first X items you need:

var array = ["one", "two", "three", "four", "five"];
var n = 3;
function shuffle(a) {
    for (let i = a.length; i; i--) {
        let j = Math.floor(Math.random() * i);
        [a[i - 1], a[j]] = [a[j], a[i - 1]];
    }
}
shuffle(array)
console.log(array.slice(0, 3))

The shuffle function was taken from this question: How can I shuffle an array?

If you still need the original array you can use slice it:

var array = ["one", "two", "three", "four", "five"];
var n = 3;
function shuffle(a) {
    for (let i = a.length; i; i--) {
        let j = Math.floor(Math.random() * i);
        [a[i - 1], a[j]] = [a[j], a[i - 1]];
    }
}
array_tmp = array.slice(0)
shuffle(array_tmp)
console.log(array_tmp.slice(0, 3))
console.log(array)

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

2 Answers2