rotate an array in JavaScript

Question

I want to rotate my entire array, for example:

[1,2,3,4] becomes [3,4,1,2]

my current function is:

function shuffle(o){ 
    for(i = 0; i<Math.floor((Math.random() * o.length)); i++){
        o.push(o.shift());
    }
};

Please tell me what I am doing wrong.

See http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array — ROMANIA_engineer, Nov 07 '14 at 15:24
Please fix your wording. ["shift"](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift) has a well-defined meaning, and so does "shuffle", they are completely different. Do you want to do one, or the other? — user229044, Nov 07 '14 at 15:25
http://dzone.com/snippets/array-shuffle-javascript That should help you. — AlvinJ, Nov 07 '14 at 15:36
@here People, you closed a question without actually letting the question's author confirm your assumptions that he is actually looking for a "shuffle". If you look at his algorithm, he's pretty clearly **rotating** the array, and his languages states he's trying to **shift** the array, so instead of editing his question so it's a duplicate and then closing it, **wait for him to clarify**. — user229044, Nov 07 '14 at 15:37
I'm sorry, just got the js-badge, and wasn't aware that one dup-vote is enough with that. I'll be more careful now. — Yoshi, Nov 07 '14 at 15:40
Yes I meant to say rotate the array, but I did not know the proper terminology — Maglor, Nov 07 '14 at 19:37

score 1 · Accepted Answer · answered Nov 07 '14 at 16:11

function shuffle(o){
    for(i = 0; i < o.length; i++)
     {
        var Index = o.indexOf(i);
        index=index+2;
        if(index>3)
        {
            index=index-2;
          var item=o.splice(index,1)
        o.push(item);
        }  
         else 

         {var item=o.splice(index,1)
          o.push(item)
        }        
}
};

score 0 · Answer 2 · answered Nov 07 '14 at 15:41

Your current function just shifts it by a random amount, i.e. it offsets it by a random amount.

Instead, you want to randomly pick from the array and move that element. Try this (untested):

function shuffle(o){
    for(i = 0; i < o.length; i++){
        var randomIndex = Math.floor(Math.random() * (o.length - i));
        var item = o.splice(randomIndex, 1);
        o.push(item);
    }
};

EDIT: It seems there's some confusion about what you're trying to accomplish. My answer above assumes you mean shuffle (randomize the order of elements in the array).

rotate an array in JavaScript

2 Answers2