How to get unique values in an array

Question

How can I get a list of unique values in an array  Do I always have to use a second array or is there something similar to java s hashmap in JavaScript   I am going to be using JavaScript and jQuery only  No additional libraries can be used

User · Answer

Majority of the solutions above have a high run time complexity.

Here is the solution that uses reduce and can do the job in O(n) time.

_x000D_

Array.prototype.unique = Array.prototype.unique || function() {_x000D_
        var arr = [];_x000D_
 this.reduce(function (hash, num) {_x000D_
  if(typeof hash[num] === 'undefined') {_x000D_
   hash[num] = 1; _x000D_
   arr.push(num);_x000D_
  }_x000D_
  return hash;_x000D_
 }, {});_x000D_
 return arr;_x000D_
}_x000D_
    _x000D_
var myArr = [3,1,2,3,3,3];_x000D_
console.log(myArr.unique()); //[3,1,2];

_x000D_

Note:

This solution is not dependent on reduce. The idea is to create an object map and push unique ones into the array.

User · Answer

These days  you can use ES6 s Set data type to convert your array to a unique Set  Then  if you need to use array methods  you can turn it back into an Array   var arr     a    a    b    var uniqueSet   new Set arr        a    b   var uniqueArr   Array from uniqueSet        a    b     Then continue to use array methods  uniqueArr join            a  b

User · Answer

One Liner  Pure JavaScript With ES6 syntax list   list filter  x  i  a    gt  a indexOf x      i  x -- gt  item in array i -- gt  index of item a -- gt  array reference   in this case  quot list quot     With ES5 syntax list   list filter function  x  i  a         return a indexOf x      i        Browser Compatibility  IE9

User · Answer

Since I went on about it in the comments for  Rocket s answer  I may as well provide an example that uses no libraries  This requires two new prototype functions  contains and unique   x000D   x000D  Array prototype contains   function v    x000D    for  var i   0  i  lt  this length  i      x000D      if  this i      v  return true  x000D      x000D    return false  x000D     x000D   x000D  Array prototype unique   function     x000D    var arr       x000D    for  var i   0  i  lt  this length  i      x000D      if   arr contains this i      x000D        arr push this i    x000D        x000D      x000D    return arr  x000D    x000D   x000D  var duplicates    1  3  4  2  1  2  3  8   x000D  var uniques   duplicates unique       result    1 3 4 2 8  x000D   x000D  console log uniques   x000D   x000D   x000D    For more reliability  you can replace contains with MDN s indexOf shim and check if each element s indexOf is equal to -1  documentation

User · Answer

Using jQuery  here s an Array unique function I made   Array prototype unique   function          var arr   this      return   grep arr  function  v  i            return   inArray v  arr      i             console log  1 2 3 1 2 3  unique         1 2 3

User · Answer

Or for those looking for a one-liner  simple and functional   compatible with current browsers    x000D   x000D  let a     1    1    2    3    3    1    x000D  let unique   a filter  item  i  ar    gt  ar indexOf item      i   x000D  console log unique   x000D   x000D   x000D    Update 18-04-2017  It appears as though  Array prototype includes  now has widespread support in the latest versions of the mainline browsers  compatibility   Update 29-07-2015   There are plans in the works for browsers to support a standardized  Array prototype includes  method  which although does not directly answer this question  is often related    Usage     1    1    2    3    3    1   includes  2           true   Pollyfill  browser support  source from mozilla       https   tc39 github io ecma262  sec-array prototype includes if   Array prototype includes      Object defineProperty Array prototype   includes         value  function searchElement  fromIndex              1  Let O be   ToObject this value         if  this    null            throw new TypeError   this  is null or not defined                   var o   Object this             2  Let len be   ToLength   Get O   length           var len   o length  gt  gt  gt  0            3  If len is 0  return false        if  len     0            return false                    4  Let n be   ToInteger fromIndex                If fromIndex is undefined  this step produces the value 0         var n   fromIndex   0            5  If n   0  then           a  Let k be n           6  Else n  lt  0            a  Let k be len   n            b  If k  lt  0  let k be 0        var k   Math max n  gt   0   n   len - Math abs n   0             7  Repeat  while k  lt  len       while  k  lt  len               a  Let elementK be the result of   Get O    ToString k               b  If SameValueZero searchElement  elementK  is true  return true             c  Increase k by 1             NOTE      provides the correct  SameValueZero  comparison needed here          if  o k      searchElement              return true                    k                      8  Return false       return false

User · Answer

You only need vanilla JS to find uniques with Array some and Array reduce  With ES2015 syntax it s only 62 characters    a reduce  c  v    gt  b some w   gt  w     v    c   c concat v    b    Array some and Array reduce are supported in IE9  and other browsers  Just change the fat arrow functions for regular functions to support in browsers that don t support ES2015 syntax   var a    1 2 3   var b    4 5 6       reduce can return a subset or superset var uniques   a reduce function c  v           some stops on the first time the function returns true                     return  b some function w   return w     v                  if there s a match  return the array  c        c                 if there s no match  then add to the end and return the entire array                                               c concat v                                            the second param in  reduce is the starting variable  This is will be  c  the first time it runs    b                                                      https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array some https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array Reduce

User · Answer

Not native in Javascript  but plenty of libraries have this method   Underscore js s   uniq array   link  works quite well  source

User · Answer

You can enter array with duplicates and below method will return array with unique elements   function getUniqueArray array       var uniqueArray           if  array length  gt  0           uniqueArray 0    array 0             for var i   0  i  lt  array length  i             var isExist   false          for var j   0  j  lt  uniqueArray length  j                 if array i     uniqueArray j                    isExist   true                  break                            else                  isExist   false                                  if isExist    false               uniqueArray uniqueArray length    array i                       return uniqueArray

User · Answer

If you don t need to worry so much about older browsers  this is exactly what Sets are designed for      The Set object lets you store unique values of any type  whether   primitive values or object references    https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Set  const set1   new Set  1  2  3  4  5  1       returns Set 5    1  2  3  4  5

User · Answer

Short and sweet solution using second array   var axes2  1 4 5 2 3 1 2 3 4 5 1 3 4        var distinct axes2          for var i 0 i lt axes2 length i                      var str axes2 i           if distinct axes2 indexOf str   -1                            distinct axes2 push str                               console log  distinct axes2     distinct axes2      distinct axes2   1 4 5 2 3

User · Answer

Using EcmaScript 2016 you can simply do it like this    var arr     a    a    b     var uniqueArray   Array from new Set arr       Unique Array   a    b      Sets are always unique  and using Array from   you can convert a Set to an array  For reference have a look at the documentations   https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array from https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Set

User · Answer

I have tried this problem in pure JS  I have followed following steps 1  Sort the given array  2  loop through the sorted array  3  Verify previous value and next value with current value     JS var inpArr    1  5  5  4  3  3  2  2  2 2  100  100  -1      sort the given array inpArr sort function a  b       return a-b       var finalArr         loop through the inpArr for var i 0  i lt inpArr length  i           check previous and next value    if inpArr i-1   inpArr i   amp  amp  inpArr i     inpArr i 1            finalArr push inpArr i          console log finalArr     Demo

User · Answer

Fast  compact  no nested loops  works with any object not just strings and numbers  takes a predicate  and only 5 lines of code    function findUnique arr  predicate      var found         arr forEach d   gt        found predicate d     d          return Object keys found  map key   gt  found key         Example  To find unique items by type   var things         name   charm   type   quark        name   strange   type   quark        name   proton   type   boson        var result   findUnique things  d   gt  d type                 name   charm   type   quark            name   proton   type   boson            If you want it to find the first unique item instead of the last add a found hasOwnPropery   check in there

User · Answer

If you want to leave the original array intact    you need a second array to contain the uniqe elements of the first-  Most browsers have Array prototype filter   var unique  array1 filter function itm  i       return array1 indexOf itm    i          returns true for only the first instance of itm         if you need a  shim   Array prototype filter  Array prototype filter    function fun  scope       var T  this  A      i  0  itm  L  T length      if typeof fun    function            while i lt L               if i in T                   itm  T i                   if fun call scope  itm  i  T   A A length   itm                              i                      return A     Array prototype indexOf  Array prototype indexOf    function what  i           if  i    typeof i    number   i  0          var L  this length          while i lt L               if this i     what  return i                i                    return -1

User · Answer

I was just thinking if we can use linear search to eliminate the duplicates   JavaScript  function getUniqueRadios      var x document getElementById  QnA    var ansArray   new Array    var prev    for  var i 0 i lt x length i               Check for unique radio button group     if  x elements i  type     radio                        For the first element prev will be null  hence push it into array and set the prev var              if  prev    null                                prev   x elements i  name                  ansArray push x elements i  name                 else                         We will only push the next radio element if its not identical to previous                     if  prev    x elements i  name                                              prev   x elements i  name                         ansArray push x elements i  name                                                     alert ansArray        HTML    lt body gt    lt form name  QnA  action    method  post    gt    lt input type  radio   name  g1  value  ANSTYPE1  gt  good  lt  input gt   lt input type  radio  name  g1  value  ANSTYPE2  gt  avg  lt  input gt    lt input type  radio   name  g2  value  ANSTYPE3  gt  Type1  lt  input gt   lt input type  radio  name  g2  value  ANSTYPE2  gt  Type2  lt  input gt     lt input type  submit  value  SUBMIT  onClick  javascript getUniqueRadios    gt  lt  input gt     lt  form gt   lt  body gt

User · Answer

Here is an approach with customizable equals function which can be used for primitives as well as for custom objects   Array prototype pushUnique   function element  equalsPredicate    l  r    gt  l    r        let res    this find item   gt  equalsPredicate item  element       if res           this push element            return res     usage     with custom equals for objects myArrayWithObjects pushUnique myObject   left  right    gt  left id    right id     with default equals for primitives myArrayWithPrimitives pushUnique somePrimitive

User · Answer

Here s a much cleaner solution for ES6 that I see isn t included here  It uses the Set and the spread operator       var a    1  1  2         new Set a     Which returns  1  2

User · Answer

Another thought of this question  Here is what I did to achieve this with fewer code    x000D   x000D  var distinctMap       x000D  var testArray     John    John    Jason    Jason    x000D  for  var i   0  i  lt  testArray length  i      x000D    var value   testArray i   x000D    distinctMap value        x000D     x000D  var unique values   Object keys distinctMap   x000D   x000D  console log unique values   x000D   x000D   x000D

User · Answer

Array prototype unique   function          var dictionary           var uniqueValues           for  var i   0  i  lt  this length  i              if  dictionary this i      undefined               dictionary this i     i              uniqueValues push this i                        return uniqueValues

[javascript] How to get unique values in an array

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