How to get an array of unique values from an array containing duplicates in JavaScript

Question

Given a   0   1   1   2   3   3   3   array  the result should be   0   1   2   3

User · Answer

You can find all kinds of array unique implementations here:

http://jsperf.com/distinct-hash-vs-comparison/12

http://jsperf.com/array-unique-functional

I prefer functional styles such as:

var arr = ['lol', 1, 'fdgdfg', 'lol', 'dfgfg', 'car', 1, 'car', 'a', 'blah', 'b', 'c', 'd', '0', '1', '1', '2', '3', '3', '3', 'crazy', 'moot', 'car', 'lol', 1, 'fdgdfg', 'lol', 'dfgfg', 'car', 1, 'car', 'a', 'blah', 'b', 'c', 'd', '0', '1', '1', '2', '3', '3', '3', 'crazy', 'moot', 'car', 'lol', 1, 'fdgdfg'];

var newarr = arr.reduce(function (prev, cur) {
    //console.log(prev, cur);
    if (prev.indexOf(cur) < 0) prev.push(cur);
    return prev;
}, []);

var secarr = arr.filter(function(element, index, array){
    //console.log(element, array.indexOf(element), index);
    return array.indexOf(element) >= index;
});

//reverses the order
var thirdarr = arr.filter(function (e, i, arr) {
    //console.log(e, arr.lastIndexOf(e), i);
    return arr.lastIndexOf(e) === i;
});

console.log(newarr);
console.log(secarr);
console.log(thirdarr);

User · Answer

This will work  Try it   function getUnique a      var b    a 0    i  j  tmp    for  i   1  i  lt  a length  i          tmp   1      for  j   0  j  lt  b length  j            if  a i     b j             tmp   0          break                    if  tmp          b push a i                return b

User · Answer

Here is the way you can do remove duplicate values from the Array   function ArrNoDupe dupArray       var temp           for  var i   0  i  lt  dupArray length  i               temp dupArray i     true           var uniqueArray              for  var k in temp             uniqueArray push k    return uniqueArray

User · Answer

function array unique nav array        nav array   nav array sort function  a  b    return a 1 - b 1                var ret    nav array 0                  Start loop at 1 as element 0 can never be a duplicate     for  var i   1  i  lt  nav array length  i               if  nav array i-1      nav array i                               ret push nav array i                                            return ret

User · Answer

Edited  ES6 solution       new Set a      Alternative   Array from new Set a      Old response  O n 2   do not use it with large arrays    var arrayUnique   function a        return a reduce function p  c            if  p indexOf c   lt  0  p push c           return p

User · Answer

If you want to maintain order   arr   arr reverse   filter function  e  i  arr        return arr indexOf e  i 1      -1     reverse      Since there s no built-in reverse indexof  I reverse the array  filter out duplicates  then re-reverse it   The filter function looks for any occurence of the element after the current index  before in the original array   If one is found  it throws out this element   Edit   Alternatively  you could use lastindexOf  if you don t care about order    arr   arr filter function  e  i  arr        return arr lastIndexOf e      i        This will keep unique elements  but only the last occurrence  This means that   0    1    0   becomes   1    0    not   0    1

User · Answer

Array prototype unique  function        var uniqObj         for var i 0 i lt  this length i           uniqObj this i   this i              return uniqObj

User · Answer

No redundant  return  array  no ECMA5  I m pretty sure   and simple to read   function removeDuplicates target array        target array sort        var i   0       while i  lt  target array length            if target array i      target array i 1                 target array splice i 1 1                     else               i    1                      return target array

User · Answer

It s 2014 now guys  and time complexity still matters   array filter function       var seen         return function element  index  array        return   element in seen   amp  amp   seen element    1                http   jsperf com array-filter-unique 13

User · Answer

Those of you who work with google closure library  have at their disposal goog array removeDuplicates  which is the same as unique  It changes the array itself  though

User · Answer

Here is an Array Prototype function   Array prototype unique   function         var unique           for  var i   0  i  lt  this length  i              if  unique indexOf this i      -1                unique push this i                        return unique

User · Answer

I like to use this  There is nothing wrong with using the for loop  I just like using the build-in functions  You could even pass in a boolean argument for typecast or non typecast matching  which in that case you would use a for loop  the filter   method function does typecast matching         Array prototype unique   function         return this filter          function val  i  arr                        return  i  lt   arr indexOf val

User · Answer

With underscorejs    uniq  1  2  1  3  1  4        gt   1  2  3  4

User · Answer

Another approach is to use an object for initial storage of the array information   Then convert back   For example   var arr     0   1   1   2   3   3   3    var obj        for var i in arr       obj i    true   arr       for var i in obj       arr push i     Variable  arr  now contains   0    1    2    3    4    5    6

User · Answer

There you go  You are welcome   Array prototype unique   function         var tmp       out           for var i   0  n   this length  i  lt  n    i                if  tmp this i      tmp this i     true  out push this i                return out     var a    1 2 2 7 4 1  a  0 6 9  a    var b   a unique    alert a   alert b

User · Answer

Array prototype unique         function    where           return function              for             var           i1   0            dups            i1  lt  this length            i1                         if     dups    where  this  this i1      length  gt  1                 for                 var               i2   dups length                --i2                this splice  dups i2   1                                                return this                         function   arr  elem             var locs                var tmpi    arr indexOf  elem  0            while               tmpi   -1              amp  amp                locs push  tmpi                tmpi   arr indexOf  elem  tmpi   1    1                                return locs

User · Answer

function array unique arr        var result           for  var i   0  i  lt  arr length  i              if  result indexOf arr i      -1                result push arr i                        return result      Not a built in function  If the product list does not contain the item  add it to unique list and return unique list

[javascript] How to get an array of unique values from an array containing duplicates in JavaScript?

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