Javascript array sort and unique

Question

I have a JavaScript array like this   var myData   237   124   255   124   366   255      I need the array elements to be unique and sorted   myData 0   124   myData 1   237   myData 2   255   myData 3   366     Even though the members of array look like integers  they re not integers  since I have already converted each to be string   var myData 0  num toString         and so on    Is there any way to do all of these tasks in JavaScript

User · Answer

I m afraid you can t combine these functions  ie  you gotta do something like this - myData unique   sort     Alternatively you can implement a kind of sortedset  as available in other languages  - which carries both the notion of sorting and removing duplicates  as you require  Hope this helps  References -  Array sort Array unique

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How about   array sort   filter function elem  index  arr      return index    arr length - 1    arr index   1     elem      This is similar to  loostro answer but instead of using indexOf which will reiterate the array for each element to verify that is the first found  it just checks that the next element is different than the current

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Another way  that does not rearrange the original Array     and spends a little less time handling duplicates   function uniqueSort arr  sortby       var A1  arr slice        A1  typeof sortby    function   A1 sort sortby   A1 sort         var last  A1 shift    next  A2   last       while A1 length           next  A1 shift            while next    last  next  A1 shift            if next  undefined               A2 A2 length   next              last  next                      return A2    var myData    237   124   255   124   366   255   100   1000    uniqueSort myData function a b  return a-b       the ordinary sort   returns the same array as the number sort here     but some strings of digits do not sort so nicely numerical

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Here is a simple one liner with O N   no complicated loops necessary    gt  Object keys   a    b    a   reduce  l  r    gt  l r    l       sort      a    b      Explanation  Original data set  assume its coming in from an external function  const data     a    b    a     We want to group all the values onto an object as keys as the method of deduplication  So we use reduce with an object as the default value      reduce fn        The next step is to create a reduce function which will put the values in the array onto the object  The end result is an object with a unique set of keys   const reduced   data reduce  l  r    gt  l r    l        We set l r    l because in javascript the value of the assignment expression is returned when an assignment statement is used as an expression  l is the accumulator object and r is the key value  You can also use Object assign l     r    l r     0    1    or something similar to get the count of each value if that was important to you   Next we want to get the keys of that object  const keys   Object keys reduced    Then simply use the built-in sort  console log keys sort      Which is the set of unique values of the original array  sorted    a    b

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This function doesn t fail for more than two duplicates values   function unique arr        var a           var l   arr length      for var i 0  i lt l  i              for var j i 1  j lt l  j                     If a i  is found later in the array             if  arr i      arr j                 j     i                    a push arr i              return a

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The solution in a more elegant way   x000D   x000D  var myData   237   124   255   124   366   255     console log Array from new Set myData   sort     x000D   x000D   x000D   I know the question is very old  but maybe someone will come in handy

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function sort unique arr        return arr sort   filter function el i a            return  i  a indexOf el

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This might be adequate in circumstances where you can t define the function in advance  like in a bookmarklet    myData sort   filter function el i a  return i   a indexOf el

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I guess I ll post this answer for some variety  This technique for purging duplicates is something I picked up on for a project in Flash I m currently working on about a month or so ago   What you do is make an object and fill it with both a key and a value utilizing each array item  Since duplicate keys are discarded  duplicates are removed   var nums    1  1  2  3  3  4  5  5  6  7  7  8  9  9  10   var newNums   purgeArray nums    function purgeArray ar        var obj           var temp           for var i 0 i lt ar length i                  obj ar i     ar i             for  var item in obj                temp push obj item              return temp      There s already 5 other answers  so I don t see a need to post a sorting function

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Here s my  more modern  approach using Array protoype reduce      2  1  2  3  reduce  a  x    gt  a includes x    a       a  x       sort      returns  1  2  3      Edit  More performant version as pointed out in the comments   arr sort   filter  x  i  a    gt   i    x    a i-1

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This is actually very simple  It is much easier to find unique values  if the values are sorted first   function sort unique arr      if  arr length     0  return arr    arr   arr sort function  a  b    return a 1 - b 1        var ret    arr 0      for  var i   1  i  lt  arr length  i        Start loop at 1  arr 0  can never be a duplicate     if  arr i-1      arr i           ret push arr i                return ret    console log sort unique   237   124   255   124   366   255          124    237    255    366

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You can now achieve the result in just one line of code   Using new Set to reduce the array to unique set of values  Apply the sort method after to order the string values   var myData   237   124   255   124   366   255    var uniqueAndSorted       new Set myData   sort      UPDATED for newer methods introduced in JavaScript since time of question

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A way to use a custom sort function    func has to return 0 in the case in which they are equal sort unique   function arr func            func   func    function  a  b                return a 1 - b 1                     arr   arr sort func           var ret    arr 0            for  var i   1  i  lt  arr length  i                  if  func arr i-1  arr i      0                   ret push arr i                                    return ret          Example  desc order for an array of objects  MyArray   sort unique MyArray   function a b               return  b iterator internal 1 - a iterator internal 1

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O N 2  solutions are bad  especially when the data is already sorted  there is no need to do two nested loops for removing duplicates  One loop and comparing to the previous element will work great   A simple solution with O   of sort   would suffice  My solution is   function sortUnique arr  compareFunction      let sorted   arr sort compareFunction     let result   sorted filter compareFunction       function val  i  a    return  i    0    compareFunction a i-1   val     0           function val  i  a    return  i    0    a i-1      val            return result      BTW  can do something like this to have Array sortUnique   method   Array prototype sortUnique   function compareFunction   return sortUnique this  compareFunction       Furthermore  sort   could be modified to remove second element if compare   function returns 0  equal elements   though that code can become messy  need to revise loop boundaries in the flight   Besides  I stay away from making my own sort   functions in interpreted languages  since it will most certainly degrade the performance  So this addition is for the ECMA 2019  consideration

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Try using an external library like underscore var f     compose   uniq  function array        return   sortBy array    identity        var sortedUnique   f array    This relies on   compose    uniq    sortBy    identity See live example What is it doing  We want a function that takes an array and then returns a sorted array with the non-unique entries removed  This function needs to do two things  sorting and making the array unique  This is a good job for composition  so we compose the unique  amp  sort function together    uniq can just be applied on the array with one argument so it s just passed to   compose the   sortBy function needs a sorting conditional functional  it expects a function that returns a value and the array will be sorted on that value  Since the value that we are ordering it by is the value in the array we can just pass the   identity function  We now have a composition of a function that  takes an array and returns a unique array  and a function that  takes an array and returns a sorted array  sorted by their values   We simply apply the composition on the array and we have our uniquely sorted array

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function sort   only is only good if your number has same digit  example   var myData     3   11   1   2     will return   var myData     1   11   2   3     and here improvement for function from mrmonkington  myData sort   sort function a b  return a - b    filter function el i a  if i  a indexOf el   amp  el length gt 0 return 1 return 0      the above function will also delete empty array and you can checkout the demo below  http   jsbin com ahojip 2 edit

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No redundant  return  array  no ECMA5 built-ins  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

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The fastest and simpleness way to do this task   const N   Math pow 8  8  let data   Array from  length   N        gt  Math floor Math random     N   let newData      let len   data length     the magic while  len--        newData data len     true

[javascript] Javascript array sort and unique

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