Remove duplicate values from a JavaScript array

This was just another solution but different than the rest.

function diffArray(arr1, arr2) {
  var newArr = arr1.concat(arr2);
  newArr.sort();
  var finalArr = [];
  for(var i = 0;i<newArr.length;i++) {
   if(!(newArr[i] === newArr[i+1] || newArr[i] === newArr[i-1])) {
     finalArr.push(newArr[i]);
   } 
  }
  return finalArr;
}

The simplest way to remove a duplicate is to do a for loop and compare the elements that are not the same and push them into the new array

 var array = ["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"];

 var removeDublicate = function(arr){
 var result = []
 var sort_arr = arr.sort() //=> optional
 for (var i = 0; i < arr.length; i++) {
        if(arr[ i + 1] !== arr[i] ){
            result.push(arr[i])
        }
 };
  return result
}  
console.log(removeDublicate(array))
==>  ["Adam", "Carl", "Jenny", "Matt", "Mike", "Nancy"]

For anyone looking to flatten arrays with duplicate elements into one unique array:

function flattenUniq(arrays) {
  var args = Array.prototype.slice.call(arguments);

  var array = [].concat.apply([], args)

  var result = array.reduce(function(prev, curr){
    if (prev.indexOf(curr) < 0) prev.push(curr);
    return prev;
  },[]);

  return result;
}

I know Im a little late, but here is another option using jinqJs

See Fiddle

var result = jinqJs().from(["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"]).distinct().select();

function arrayDuplicateRemove(arr){
    var c = 0;
    var tempArray = [];
    console.log(arr);
    arr.sort();
    console.log(arr);
    for (var i = arr.length - 1; i >= 0; i--) {
        if(arr[i] != tempArray[c-1]){
            tempArray.push(arr[i])
            c++;
        }
    };
    console.log(tempArray);
    tempArray.sort();
    console.log(tempArray);
}

This is probably one of the fastest way to remove permanently the duplicates from an array

It is 10 times faster than the most functions here. And 78 times faster in Safari.

function toUnique(a, b, c) { // array, placeholder, placeholder
  b = a.length;
  while (c =-- b)
    while (c--)
      a[b] !== a[c] || a.splice(c, 1)
}

1. Test: http://jsperf.com/wgu
2. Demo: http://jsfiddle.net/46S7g/
3. More: https://stackoverflow.com/a/25082874/2450730

If you can't read the code above, ask, read a JavaScript book or here are some explanations about shorter code. How to 'minify' Javascript code

The easiest way to remove string duplicates is to use associative array and then iterate over the associative array to make the list/array back.

Like below:

var toHash = [];
var toList = [];

// add from ur data list to hash
$(data.pointsToList).each(function(index, Element) {
    toHash[Element.nameTo]= Element.nameTo;
});

// now convert hash to array
// don't forget the "hasownproperty" else u will get random results 
for (var key in toHash)  {
    if (toHash.hasOwnProperty(key)) { 
      toList.push(toHash[key]);
   }
}

Voila, now duplicates are gone!

This solution uses a new array, and an object map inside the function. All it does is loop through the original array, and adds each integer into the object map.If while looping through the original array it comes across a repeat, the

`if (!unique[int])`

catches this because there is already a key property on the object with the same number. Thus, skipping over that number and not allowing it to be pushed into the new array.

    function removeRepeats(ints) {
      var unique = {}
      var newInts = []

      for (var i = 0; i < ints.length; i++) {
        var int = ints[i]

        if (!unique[int]) {
          unique[int] = 1
          newInts.push(int)
        }
      }
      return newInts
    }

    var example = [100, 100, 100, 100, 500]
    console.log(removeRepeats(example)) // prints [100, 500]

Here are some vanilla JS solutions with a complexity of O(n) (fastest possible for this problem). Modify the hashFunction to distinguish the objects (e.g., 1 and "1") if needed. The first solution avoids hidden loops (common in functions provided by Array).

var dedupe = function(a)
{
    var hash = {}, ret = [];
    var hashFunction = function(v) { return ""+v; };
    var collect = function(h)
    {
        if(hash.hasOwnProperty(hashFunction(h)) == false) // O(1)
        {
            hash[hashFunction(h)]=1;
            ret.push(h); // Should be O(1) for Arrays
            return;
        }
    };

    for(var i=0; i<a.length; i++) // This is a loop: O(n)
        collect(a[i]);
    // OR: a.forEach(collect); // This is a loop: O(n)

    return ret;
}

var dedupe = function(a)
{
    var hash = {};
    var isdupe = function(h)
    {
        if(hash.hasOwnProperty(h) == false) // O(1)
        {
            hash[h] = 1;
            return true;
        }

        return false;
    };

    return a.filter(isdupe); // This is a loop: O(n)
}

Here is a nested loop method for removing duplicates in array and preserving original order of elements.

var array = [1, 3, 2, 1, [5], 2, [4]]; // INPUT

var element = 0;
var decrement = array.length - 1;
while(element < array.length) {
  while(element < decrement) {
    if (array[element] === array[decrement]) {
      array.splice(decrement, 1);
      decrement--;
    } else {
      decrement--;
    }
  }
  decrement = array.length - 1;
  element++;
}

console.log(array);// [1, 3, 2, [5], [4]]

Explanation: The inner loop compares first element of array with all other elements starting with element at the highest index. Decrementing towards the first element, a duplicate is spliced from the array.

When the inner loop is finished, the outer loop increments to the next element for comparison and resets the new length of the array.

Here is another approach using jQuery,

function uniqueArray(array){
  if ($.isArray(array)){
    var dupes = {}; var len, i;
    for (i=0,len=array.length;i<len;i++){
      var test = array[i].toString();
      if (dupes[test]) { array.splice(i,1); len--; i--; } else { dupes[test] = true; }
    }
  } 
  else {
    if (window.console) console.log('Not passing an array to uniqueArray, returning whatever you sent it - not filtered!');
      return(array);
  }
  return(array);
}

Author: William Skidmore

function removeDuplicates(inputArray) {
            var outputArray=new Array();

            if(inputArray.length>0){
                jQuery.each(inputArray, function(index, value) {
                    if(jQuery.inArray(value, outputArray) == -1){
                        outputArray.push(value);
                    }
                });
            }           
            return outputArray;
        }

If you don't want to include a whole library, you can use this one off to add a method that any array can use:

Array.prototype.uniq = function uniq() {
  return this.reduce(function(accum, cur) { 
    if (accum.indexOf(cur) === -1) accum.push(cur); 
    return accum; 
  }, [] );
}

["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"].uniq()

If you're creating the array yourself, you can save yourself a loop and the extra unique filter by doing the check as you're inserting the data;

var values = [];
$.each(collection, function() {
    var x = $(this).value;
    if (!$.inArray(x, values)) {
        values.push(x);
    }
});

function removeDuplicates (array) {
  var sorted = array.slice().sort()
  var result = []

  sorted.forEach((item, index) => {
    if (sorted[index + 1] !== item) {
      result.push(item)
    }
  })
  return result
}

aLinks is a simple JavaScript array object. If any element exist before the elements on which the index shows that a duplicate record deleted. I repeat to cancel all duplicates. One passage array cancel more records.

var srt_ = 0;
var pos_ = 0;
do {
    var srt_ = 0;
    for (var i in aLinks) {
        pos_ = aLinks.indexOf(aLinks[i].valueOf(), 0);
        if (pos_ < i) {
            delete aLinks[i];
            srt_++;
        }
    }
} while (srt_ != 0);

var uniqueCompnies = function(companyArray) {
    var arrayUniqueCompnies = [],
        found, x, y;

    for (x = 0; x < companyArray.length; x++) {
        found = undefined;
        for (y = 0; y < arrayUniqueCompnies.length; y++) {
            if (companyArray[x] === arrayUniqueCompnies[y]) {
                found = true;
                break;
            }
        }

        if ( ! found) {
            arrayUniqueCompnies.push(companyArray[x]);
        }
    }

    return arrayUniqueCompnies;
}

var arr = [
    "Adobe Systems Incorporated",
    "IBX",
    "IBX",
    "BlackRock, Inc.",
    "BlackRock, Inc.",
];

var lines = ["Mike", "Matt", "Nancy", "Adam", "Jenny", "Nancy", "Carl"];
var uniqueNames = [];

for(var i = 0; i < lines.length; i++)
{
    if(uniqueNames.indexOf(lines[i]) == -1)
        uniqueNames.push(lines[i]);
}
if(uniqueNames.indexOf(uniqueNames[uniqueNames.length-1])!= -1)

for(var i = 0; i < uniqueNames.length; i++)
{
    document.write(uniqueNames[i]);
      document.write("<br/>");
}

Quick and easy using Lodash:

var array = ["12346", "12347", "12348", "12349", "12349"];
console.log(_.uniqWith(array, _.isEqual));

var duplicates = function(arr){
     var sorted = arr.sort();
   var dup = [];
   for(var i=0; i<sorted.length; i++){
        var rest  = sorted.slice(i+1); //slice the rest of array
       if(rest.indexOf(sorted[i]) > -1){//do indexOf
            if(dup.indexOf(sorted[i]) == -1)    
         dup.push(sorted[i]);//store it in another arr
      }
   }
   console.log(dup);
}

duplicates(["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"]);