Removing duplicate element in an array

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Easiest way to find duplicate values in a JavaScript array
Javascript array sort and unique

I have the following array

var output = new array(7);
  output[0]="Rose";
  output[1]="India";
  output[2]="Technologies";
  output[3]="Rose";
  output[4]="Ltd";
  output[5]="India";
  output[6]="Rose";

how can i remove the duplicate elements in above array.Is there any methods to do it?

What have you tried? There is no function natively available, but it isn't very hard to write yourself. — Halcyon, Mar 17 '12 at 15:57
This is been asked already.. http://stackoverflow.com/questions/2218999/remove-duplicates-from-an-array-of-objects-in-javascript And the solution there is really clever and good.. — Prasanna, Mar 17 '12 at 16:02
i tried for (var i = 0; i < output.length - 1; i++) { if (sorted_arr[i + 1] == sorted_arr[i]) { results.push(sorted_arr[i]); } } — vishnu, Mar 17 '12 at 16:07

score 9 · Accepted Answer · answered Mar 17 '12 at 16:10

9

You can write a function like this

function eliminateDuplicates(arr) {
var i,
  len=arr.length,
  out=[],
  obj={};

 for (i=0;i<len;i++) {
 obj[arr[i]]=0;
 }
 for (i in obj) {
 out.push(i);
 }
 return out;
}`

Check this here

answered Mar 17 '12 at 16:10

asitmoharna

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score 3 · Answer 2 · answered Mar 17 '12 at 15:57

Maybe more complex than you need but:

function array_unique (inputArr) {
    // Removes duplicate values from array  
    var key = '',
        tmp_arr2 = {},
        val = '';

    var __array_search = function (needle, haystack) {
        var fkey = '';
        for (fkey in haystack) {
            if (haystack.hasOwnProperty(fkey)) {
                if ((haystack[fkey] + '') === (needle + '')) {
                    return fkey;
                }
            }
        }
        return false;
    };

    for (key in inputArr) {
        if (inputArr.hasOwnProperty(key)) {
            val = inputArr[key];
            if (false === __array_search(val, tmp_arr2)) {
                tmp_arr2[key] = val;
            }
        }
    }

    return tmp_arr2;
}

Code taken from: http://phpjs.org/functions/array_unique:346

Don't you think that might a *bit* overcomplicated for the OP? He's obviously just getting into Javascript. Then again, he could just copy-paste and let the magic function do its trick, but that's not very helpful or in the spirit of good learning... — Elliot Bonneville, Mar 17 '12 at 16:02
It's a complex thing to be doing just if you are just starting out. I assumed he needed a copy-paste solution. — nathanjosiah, Mar 17 '12 at 16:03

score 1 · Answer 3 · edited Mar 17 '12 at 16:18

1

First of all, you'll want to use the array literal (var output = []) to declare your array. Second, you'll want to loop through your array and store all the values in a second array. If any value in the first array matches a value in the second array, delete it and continue looping.

Your code would look like this:

var output = [
    "Rose",
    "India",
    "Technologies",
    "Rose",
    "Ltd",
    "India",
    "Rose"
]

var doubledOutput = [];

for(var i = 0; i < output.length; i++) {
    var valueIsInArray = false;

    for(var j = 0; j < doubledOutput.length; j++) {
        if(doubledOutput[j] == output[i]) {
            valueIsInArray = true;
        }
    }

    if(valueIsInArray) {
        output.splice(i--, 1);
    } else {
        doubledOutput.push(output[i]);
    }
}

Please note, the above code is untested and may contain errors.

edited Mar 17 '12 at 16:18

pimvdb

151,816
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answered Mar 17 '12 at 15:56

Elliot Bonneville

51,872
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Can I ask the reason for the unexplained downvote? It's just a simple, readable, and easy way of finding duplicate values for a beginner in Javascript who obviously doesn't need a complicated and overworked solution. – Elliot Bonneville Mar 17 '12 at 16:01
I didn't downvote, but you're both incrementing `i` *and* deleting items. You'll be missing elements that way, unless you decrement `i` a well when splicing an element. – pimvdb Mar 17 '12 at 16:05
Oops, yeah, I should have used a reverse loop. My bad, thanks for the catch. – Elliot Bonneville Mar 17 '12 at 16:06
In fact I think you meant to change `valueIsInArray` to `true` and to actually populate `doubledOutput`... – pimvdb Mar 17 '12 at 16:08
Guilty as charged. I wrote up the code really quickly so as to get the answer in before somebody else... doesn't help that I haven't had my coffee yet either. Fixing all counts. :) – Elliot Bonneville Mar 17 '12 at 16:10
A little friendly advice... before you criticize another answer for not being *"in the spirit of good learning"*, make sure your own is correct. I don't think a *"Please note, the above code is untested and may contain errors."* warning is helpful to a beginner. – Mar 17 '12 at 16:15
...I assume you meant to do `var i = output.length - 1` so you don't start outside the length of the array. – Mar 17 '12 at 16:16
...also, an Array doesn't have an `.append()` method, and nothing will be added to the `doubledOutput` Array. – Mar 17 '12 at 16:19
http://i2.kym-cdn.com/entries/icons/original/000/000/554/facepalm.jpg You know what, next time I'm just going to test my code first. – Elliot Bonneville Mar 17 '12 at 16:38

jfriend00 · Answer 4 · 2012-03-17T16:07:10.923

You can remove dups from an array by using a temporary hash table (using a javascript object) to keep track of which images you've already seen in the array. This works for array values that can be uniquely represented as a string (strings or numbers mostly), but not for objects.

function removeDups(array) {
    var index = {};
    // traverse array from end to start 
    // so removing the current item from the array
    // doesn't mess up the traversal
    for (var i = array.length - 1; i >= 0; i--) {
        if (array[i] in index) {
            // remove this item
            array.splice(i, 1);
        } else {
            // add this value to index
            index[array[i]] = true;
        }
    }
}

Here's a working example: http://jsfiddle.net/jfriend00/sVT7g/

For sizable arrays, using an object as a temporary index will be many times faster than a linear search of the array.

Removing duplicate element in an array

4 Answers4

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