Swapping two items in a javascript array

Question

Possible Duplicate:
Javascript swap array elements

I have a array like this:

this.myArray = [0,1,2,3,4,5,6,7,8,9];

Now what I want to do is, swap positions of two items give their positions. For example, i want to swap item 4 (which is 3) with item 8 (which is 7) Which should result in:

this.myArray = [0,1,2,7,4,5,6,3,8,9];

How can I achieve this?

Duplicate (with some outrageous solutions for your amusement) - http://stackoverflow.com/questions/872310/javascript-swap-array-elements — Chetan S, Oct 25 '10 at 03:01

kennebec · Answer 1 · 2013-05-09T04:29:49.730

123

The return value from a splice is the element(s) that was removed-

no need of a temp variable

Array.prototype.swapItems = function(a, b){
    this[a] = this.splice(b, 1, this[a])[0];
    return this;
}

var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

alert(arr.swapItems(3, 7));

returned value: (Array)

    0,1,2,7,4,5,6,3,8,9

edited May 09 '13 at 04:29

answered Oct 25 '10 at 04:10

kennebec

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1

Nice!! How come no one else has voted this answer up. – zachzurn Nov 22 '11 at 08:02
The key for understanding that solution is that splice() can have additional items after start and deleteCount which will get inserted at the splicing position. Only one blemish: splice() returns an array, so to get the one (and only) element from that array, one would have to say: `this[a]= this.splice(b, 1, this[a])[0];` – trembl Dec 08 '11 at 07:11
19

Consider this as well, splice is O(n), http://stackoverflow.com/questions/11514308/big-o-of-javascript-arrays – Nick Apr 05 '14 at 18:33

Michael Aaron Safyan · Accepted Answer · 2015-09-24T09:50:16.447

Just reassign the elements, creating an intermediate variable to save the first one you over-write:

var swapArrayElements = function(arr, indexA, indexB) {
  var temp = arr[indexA];
  arr[indexA] = arr[indexB];
  arr[indexB] = temp;
};
// You would use this like: swapArrayElements(myArray, 3, 7);

If you want to make this easier to use, you can even add this to the builtin Array prototype (as kennebec@ suggests); however, be aware that this is generally a bad pattern to avoid (since this can create issues when multiple different libraries have different ideas of what belongs in the builtin types):

Array.prototype.swap = function(indexA, indexB) {
   swapArrayElements(this, indexA, indexB);
};
// You would use this like myArray.swap(3, 7);

Note that this solution is significantly more efficient than the alternative using splice(). (O(1) vs O(n)).

without mutation: `const swapArrayElements = (arr, a, b) => { let _arr = [...arr]; let temp = _arr[a]; _arr[a] = _arr[b]; _arr[b] = temp; return _arr }` — Ed Williams, Apr 23 '18 at 13:37

score 5 · Answer 3 · answered Oct 25 '10 at 02:58

You can just use a temp variable to move things around, for example:

var temp = this.myArray[3];
this.myArray[3] = this.myArray[7];
this.myArray[7] = temp;

You can test it out here, or in function form:

Array.prototype.swap = function(a, b) {
  var temp = this[a];
  this[a] = this[b];
  this[b] = temp;
};

Then you'd just call it like this:

this.myArray.swap(3, 7);

You can test that version here.

Swapping two items in a javascript array

3 Answers3

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