Array.unique

JavaScript performance comparison

Test case created by Marco Demaio

Info

Testing 2 functions to remove duplicates in Array.

The 1st function Array.unique remove deuplicates by simply using a nested for loop

The 2nd function Array.unique2 uses removes duplicates by using Array.indexOf

Preparation code

<script>
  /**************************************************************************************************
   Search an element in the array and returns its index if found or -1 if not found.
   FF 1.5+ already implements this method. Using the native method is definitely faster therefor is better to add an if test to see if the methos is already defined.
   [sources: https://developer.mozilla.org/en/New_in_JavaScript_1.6
   https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf#Compatibility]
   **************************************************************************************************/
  if (!Array.prototype.indexOf) Array.prototype.indexOf = function(val) {
   //Reversed loop are much faster [source: http://stackoverflow.com/questions/3520688/javascript-loop-performance-why-is-to-decrement-the-iterator-toward-0-faster-th/ and http://blogs.sun.com/greimer/entry/best_way_to_code_a]
   var i = this.length;
   while (i--)
   if (this[i] === val) return i;
  
   return -1;
  }
  
  /**************************************************************************************************
   Returns a new array where all duplicates has been removed.
   On sortable arrays there are faster ways to remove duplicates [ref. http://stackoverflow.com/questions/840781/easiest-way-to-find-duplicate-values-in-a-javascript-array/840812#840812], but this is a generic function and the array is not necessarely sortable (i.e. an array of HTML elements, how do you sort it).
   **************************************************************************************************/
  Array.prototype.unique = function() {
   var result = [],
       i, j, l1 = this.length,
       l2, dupe;
  
   //Adding 1st element to result, than one by one all other elements. Before adding each element we check that is not already present in result.
   for (i = 0; i < l1; ++i) {
    dupe = false;
    for (j = 0, l2 = result.length; j < l2; ++j) {
     //If dupe element is found we don't add the element to the result.
     if (result[j] === this[i]) {
      dupe = true;
      break;
     }
    }
    if (!dupe) result[result.length] = this[i];
   }
  
   return result;
  };
  
  /**************************************************************************************************
   Returns a new array where all duplicates has been removed.
   It's the same of Array.unique, but this time we use Array.indexOf to find duplicates.
   **************************************************************************************************/
  Array.prototype.unique2 = function() {
   var result = [],
       i, j, l1 = this.length,
       l2, dupe;
  
   //Adding 1st element to result, than one by one all other elements. Before adding each element we check that is not already present in result.
   for (i = 0; i < l1; ++i)
   //If dupe element is found we don't add the element to the result.
   if (result.indexOf(this[i]) === -1) result[result.length] = this[i];
  
   return result;
  };
  
  var v1 = [];
  
  //Filling a vector with 10000 random value in the range 1-10 inclusive
  for (i = 0; i < 10000; i++)
  v1[i] = Math.floor(10 * Math.random()) + 1;
</script>

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Testing in unknown unknown
Test Ops/sec
Remove duplicates without using Array.indexOf
 
v2 = v1.unique();
 pending…
Remove duplicates using Array.indexOf
 
v2 = v1.unique2();
 pending…

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