jQuery select random elements with same class

Question

I have elements with class "selectElement". When I click on element with that class, I "select" it, and give it another class "selectedElements", if it doesn't already have it.

But, I have a button that should randomly select certain number (e.g. 10) of elements with class "selectElement" and give them the "selectedElement" class.

I tried something like in this answer -> https://stackoverflow.com/a/1764629/1011539, but it returns same values every time...

EDIT: Solved with Jon's help. Here is the code for other users with similar problem :)

$("#chooseElementsRand").live("click",function(){
    $(".selectedElements").removeClass("selectedElements");
    var maxNum = parseInt($(".maxNum").html());
    var randomElements = shuffle($(".selectElement")).slice(0,maxNum).addClass("selectedElements");
    $(".selectedNum").html(randomElements.length);
    if(randomElements.length==maxNum) {
        $(".buttonToProceed").removeClass("notShown");
    }
});

Solution 1

Whenever you want to pick N elements really at random out of X, the solution is the Fisher-Yates shuffle. This page has a Javascript implementation (plus rationale, plus nice animations, so go have a look):

function shuffle(array) {
  var m = array.length, t, i;

  // While there remain elements to shuffle…
  while (m) {

    // Pick a remaining element…
    i = Math.floor(Math.random() * m--);

    // And swap it with the current element.
    t = array[m];
    array[m] = array[i];
    array[i] = t;
  }

  return array;
}

Given the shuffle, you can then pick X elements at random with

var items = shuffle($(".selectElement")).slice(0, X);

Here's a working fiddle to play with.

Footnote: since you are only interested in a certain amount of random picks, there's no need to unconditionally shuffle the whole input array as shuffle does above; you could shuffle only a small part and then use .slice to cut it off and work with it. I 'm leaving this as an exercise; be careful that you don't grab the *un*shuffled part by mistake!

Solution 2

You can select random item by class name using jquery method eq()

see the example bellow.

var len = $(".someClass").length;
var random = Math.floor( Math.random() * len ) + 1;
$(".someClass").eq(random).css("background-color", "yellow");

Solution 3

Something like this would work (Trigger it by clicking on an element)

$(".selectElement").on("click", function() {
    var randomElements = $(".selectElement").get().sort(function() {
        return Math.round(Math.random()) - 0.5;
    }).slice(0, 5);
    $(randomElements).css('border', '1px solid red');
});​

http://jsfiddle.net/rKFfm/

Comments

[kichik]

This is my favorite answer here because it doesn't require accessing the entire list, but the + 1 means you'll never get the first item in the list.

[PsychoMantis]

This is nice, I added this line after the random declaration to allow a chance to select the first item: random = ((Math.random() * 10)+1) > 5 ? random + 1 : random;

[Avatar]

Useful: function getRandomInt(min, max) at stackoverflow.com/a/1527820/1066234