Array Remove Duplicate Results Javascript

Question

I need to remove the duplicates after they are shuffled. Currently the results come out with duplicates.

Example: Results 2,2,1,4,4,3,5,5, I need as 2,1,4,3,5

This is a large array

<script>
Array.prototype.shuffle = function() {
var input = this;

for (var i = input.length-1; i >=0; i--) {

    var randomIndex = Math.floor(Math.random()*(i+1)); 
    var itemAtIndex = input[randomIndex]; 

    input[randomIndex] = input[i]; 
    input[i] = itemAtIndex;

}
return input;
}

var tempArray = [ 

1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,

2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,

3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,

4,4,4,4,4,4,4,4,4,4,4,4,4,

5,5,5,5,5,
]

tempArray.shuffle();

document.write(tempArray);

</script>

@MarkF Please choose a best answer by clicking on the check mark next to it. It helps a lot. — David G
– David G, Commented Aug 28, 2012 at 22:39
I still can not get it to remove the duplicates. Can you put your code inside my script to make sure I am putting it inside my script correctly? — Mark F
– Mark F, Commented Aug 28, 2012 at 23:56
@MarkF Please choose a best answer by clicking on the checkmark next to it. It helps a lot. — David G
– David G, Commented Aug 31, 2012 at 22:30

João Silva · Accepted Answer · 2012-08-28 19:41:32Z

3

Instead of using that large array, simply use [1,2,3,4,5].shuffle(). This way, you won't get duplicates. But here's a function that will give you a unique array, i.e., an array without duplicates:

function unique(arr) {
  var result = [],
      map = {};
  for (var i = 0; i < arr.length; i++) {
    var duplicate = map[arr[i]];
    if (!duplicate) {
        result.push(arr[i]);
        map[arr[i]] = true;
    }
  }
  return result;
}

Then, just use unique(tempArray.shuffle()).

Here's a DEMO.

edited Aug 28, 2012 at 19:41

answered Aug 28, 2012 at 19:32

João Silva

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2 Comments

Mark F Over a year ago

I need to use all the numbers. They are weighted.

João Silva Over a year ago

@MarkF: I've updated my answer, you can use unique() to remove duplicates.

Ry- · Accepted Answer · 2012-08-30 15:20:32Z

2

function unique(b) {
    for (var c = [], d = {}, a = 0; a < b.length; a++) {
        d[b[a]] || (c.push(b[a]), d[b[a]] = !0);
    }
    return c;
}

unique( [1, 1, 1, 2, 2, 3] ); // [1, 2, 3]

edited Aug 30, 2012 at 15:20

Ry-♦

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answered Aug 28, 2012 at 19:48

David G

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3 Comments

Ry- Over a year ago

Did you seriously just minify @João's answer?

David G Over a year ago

No. I minified my own. I know it has the same function name and everything. Should I change it?

Ry- Over a year ago

No, don't worry, just wondering (they compile to the same thing under Google Closure Compiler).

Dan Porat · Accepted Answer · 2017-11-09 08:22:10Z

1

You can use the following approach, using ES6 syntax: const unique = [...new Set(array)]

More about the Set object: Mozilla - Set object

answered Nov 9, 2017 at 8:22

Dan Porat

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Comments

Nick Briz · Accepted Answer · 2012-08-29 16:01:31Z

0

If you have access to jQuery, you could split the process into two arrays, take that result, loop through it and only add it to the newArray if it's not already in there. This way they come out in the same order.

var someArray = [3,3,3,3,3,3,4,4,4,4,1,1,1,1,1,2,2];

function cleanArray(oldArray) {
    var newArray = [];
    for(i=0;i<oldArray.length;i++) {
        if( $.inArray(oldArray[i], newArray) == -1 ) {
            newArray.push(oldArray[i]);         
        }
    }
    return newArray;
}

document.write(cleanArray(someArray));
//result would be 3,4,1,2

EDIT: I've updated the function so it works the way I believe you imagined. Here's a working example: http://jsfiddle.net/xe2F8/

Also, don't forget to link to jquery:

    <script src="http://code.jquery.com/jquery-latest.js"></script>

edited Aug 29, 2012 at 16:01

answered Aug 28, 2012 at 19:52

Nick Briz

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2 Comments

Nick Briz Over a year ago

you're right, jQuery is just so ubiquitous at this point, I figure most folks will be using it + will recognize the $ when they see it... but this isn't always the case (nor does $ === jQuery) ... so I shouldn't assume, thnx for the edit.

Mark F Over a year ago

How do I call the function using document.write

Narayanan R · Accepted Answer · 2017-11-09 06:52:24Z

0

One really quick way of removing duplicates from any JavaScript array is the following:

var listWithDuplicates = [1, 2, 2, 4, 3, 4, 5, 3, 1, 5];
console.log(listWithDuplicates.filter(function(element, index, array) {
  // using lastIndexOf(...) retains the last
  // repetition preserving the order of the array
  return index === array.indexOf(element);
}));
//prints out: [1, 2, 4, 3, 5] - with indexOf variant
//prints out: [2, 4, 3, 1, 5] - with lastIndexOf variant

Hope this comes in handy for some purpose related to removing duplicates from JavaScript arrays.

Please share feedback about any corner cases not addressed by this solution or any suggestions for improving this answer.

edited Nov 9, 2017 at 6:52

answered Nov 9, 2017 at 6:44

Narayanan R

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