How to efficiently randomly select array item without repeats?

Question

I'm aware that this question is around in many guises but I have not been able to find an answer relating to my specific issue of efficiency.

I have the below code that works just fine.

I have a 10 item array from which I randomly select an item (on enter key press). The code keeps an array of the 5 most recent choices which cannot be randomly selected (to avoid too much repetition over time).

If the chooseName() function initially selects a name that has been used in the recent 5 goes it simply breaks and calls itself again, repeating until it finds a "unique" name.

I have two questions:

1. Is it correct to say this is a "recursive function"?

2. I am worried that theoretically this could keep looping for a long time before finding a unique name - is there a more efficient way to do this?

Thank you for any help.

    var a = ["Roger", "Russell", "Clyde", "Egbert", "Clare", "Bobbie", "Simon", "Elizabeth", "Ted", "Caroline"];
    var b = [];

    var chooseName = function () {
    var unique = true;
    b.length = 5;
    num = Math.floor(Math.random() * a.length);
    name = a[num];    
        for (i = 0; i < a.length; i++) {
        if (b[i] == name) {
            chooseName();
            unique = false;
            break;
            }
        }
        if (unique == true) {
        alert(name);
        b.unshift(name);
        }
    }


    window.addEventListener("keypress", function (e) {
        var keycode = e.keyCode;
        if (keycode == 13) {
        chooseName();
        }
    }, false);

Answer 1

I like commenter @YuriyGalanter's idea of choosing items randomly until all are taken and only then repeating, so here's an implementation:

function randomNoRepeats(array) {
  var copy = array.slice(0);
  return function() {
    if (copy.length < 1) { copy = array.slice(0); }
    var index = Math.floor(Math.random() * copy.length);
    var item = copy[index];
    copy.splice(index, 1);
    return item;
  };
}

var chooser = randomNoRepeats(['Foo', 'Bar', 'Gah']);
chooser(); // => "Bar"
chooser(); // => "Foo"
chooser(); // => "Gah"
chooser(); // => "Foo" -- only repeats once all items are exhausted.

Answer 2

Whenever an item is selected, move it to the back of the array and randomly select from a slice of the original array array.slice(0, -5).

var a = ["Roger", "Russell", "Clyde", "Egbert", "Clare", "Bobbie", "Simon", "Elizabeth", "Ted", "Caroline"];

var chooseName = function () {
    var unique = true;
    num = Math.floor(Math.random() * a.length - 5);
    name = a.splice(num,1);
    a.push(name);
}


window.addEventListener("keypress", function (e) {
    var keycode = e.keyCode;
    if (keycode == 13) {
        chooseName();
    }
}, false);

EDIT: This also has the side-effect of not giving whichever variables happen to tail the list the unfair disadvantage that they won't be considered in the first N calls. If that's a problem for you, maybe try hold a static variable somewhere to keep track of the size of the slice to use and max it out at B (in this case, 5). e.g.

var a = ["Roger", "Russell", "Clyde", "Egbert", "Clare", "Bobbie", "Simon", "Elizabeth", "Ted", "Caroline"];
B = 5; //max size of 'cache'
N = 0;

var chooseName = function () {
    var unique = true;
    num = Math.floor(Math.random() * a.length - N);
    N = Math.min(N + 1, B);
    name = a.splice(num,1);
    a.push(name);
}