select random value NOT in array

Question

How would I select a random value (0 to 30) that is not in this array?

var list = new Array(1,3,4,7,8,9);

Answer 1

A little recursive function:

getNum() {
  let randomNum = Math.floor(Math.random() * (30 - 1)) + 1
  if (list.includes(randomNum)) {
    return getNum()
  }
   return randomNum
}

Might be a little faster, since it first tries to return a random number, and then checks if it's in the array.

Answer 2

Build the complementary array and pick random values from it.

var list2 = new Array();
for(var i=0; i<30; i++)
  if(!list.contains(i))
    list2.push(i);

Then:

var rand = list2[Math.floor(Math.random() * list2.length)];

Answer 3

Assuming your list is reasonable small in size, create a list of numbers that are not in the array and then select a number from that array at random.

Answer 4

You need a while loop that tests if rand is in your restricted array and, if so, re-generate a new random number:

var rand;
do {
    rand = Math.floor(Math.random() * 31); // re-randomize, 0 to 30 inclusive
} while ($.inArray(rand, restricted) > -1);
return rand;

http://jsfiddle.net/mblase75/dAN8R/

Don't want jQuery? You can replace $.inArray(rand, restricted) with restricted.indexOf(rand) if you use this polyfill for old browsers.

Answer 5

function RandomValueNotInArray(array)
{
    var e;
    do
    {
        e = Math.random() * 31; // n + 1
    } while (array.contains(e))
    return e;
}