Removing duplicate objects with Underscore for Javascript

Question

I have this kind of array   var foo        a     1        b     2        a     1         I d like to filter it to have   var bar        a     1        b     2        I tried using   uniq  but I guess because    a     1    is not equal to itself  it doesn t work  Is there any way to provide underscore uniq with an overriden equals function

User · Answer

Using underscore unique lib following is working for me  I m making list unique on the based of  id then returning String value of  id   var uniqueEntities     uniq entities  function  item  key  a                                        return item  id toString

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You can do it in a shorthand as      uniq foo   a

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Try iterator function  For example you can return first element  x      a  1    b  2    a  1      uniq x false function i         return i 0       a   b                 a  1    b  2

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Implementation of Shiplu s answer   var foo        a     1        b     2        a     1        var x     uniq    collect  foo  function  x        return JSON stringify  x          console log  x       returns      a     1        b     2

User · Answer

here s my solution  coffeescript       mixin   deepUniq   coll  - gt      result          remove first el duplicates    coll2  - gt         rest     rest coll2        first     first coll2        result push first       equalsFirst    el  - gt    isEqual el first         newColl     reject rest  equalsFirst        unless   isEmpty newColl         remove first el duplicates newColl      remove first el duplicates coll      result   example     deepUniq    a 1 b 12     2  1  2  1      1  2  1  2     2  1  2  1     a 1 b 12          gt      a  1  b  12      2  1  2  1      1  2  1  2

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var foo        a     1        b     2        a     1       var bar     map   groupBy foo  function  f             return JSON stringify f            function  gr             return gr 0               Lets break this down  First lets group the array items by their stringified value  var grouped     groupBy foo  function  f         return JSON stringify f          grouped looks like             a     1            a     1       a     1               b     2            b     2          Then lets grab the first element from each group  var bar     map grouped  function gr      return gr 0          bar looks like       a     1        b     2       Put it all together   var foo        a     1        b     2        a     1       var bar     map   groupBy foo  function  f             return JSON stringify f            function  gr             return gr 0

User · Answer

Here is a simple solution  which uses a deep object comparison to check for duplicates  without resorting to converting to JSON  which is inefficient and hacky   var newArr     filter oldArr  function  element  index           tests if the element has a duplicate in the rest of the array     for index    1  index  lt  oldArr length  index    1            if    isEqual element  oldArr index                  return false                      return true        It filters out all elements if they have a duplicate later in the array - such that the last duplicate element is kept   The testing for a duplicate uses   isEqual which performs an optimised deep comparison between the two objects see the underscore isEqual documentation for more info   edit  updated to use   filter which is a cleaner approach

User · Answer

If you re looking to remove duplicates based on an id you could do something like this   var res        id  1  content   heeey       id  2  content   woah        id  1  content  foo       id  1  content   heeey       var uniques     map   groupBy res function doc     return doc id     function grouped     return grouped 0          uniques     id  1  content   heeey    id  2  content   woah

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When I have an attribute id  this is my preffered way in underscore   var x     i 2    i 2  x 42    i 4    i 3      chain x  indexBy  i   values   value        gt    i 2  x 42    i 4    i 3

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with underscore i had to use String   in the iteratee function  function isUniq item        return String item user     var myUniqArray     uniq myArray  isUniq

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uniq  unique accepts a callback  var list     a 1 b 5   a 1 c 5   a 2   a 3   a 4   a 3   a 2     var uniqueList     uniq list  function item  key  a         return item a          uniqueList    Object  a 1  b 5   Object  a 2   Object  a 3   Object  a 4     Notes    Callback return value used for comparison First comparison object with unique return value used as unique underscorejs org demonstrates no callback usage lodash com shows usage   Another example    using the callback to extract car makes  colors from a list

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I wanted to solve this simple solution in a straightforward way of writing  with a little bit of a pain of computational expenses    but isn t it a trivial solution with a minimum variable definition  is it   function uniq ArrayObjects     var out        ArrayObjects map obj   gt        if   every out  outobj   gt     isEqual obj  outobj    out push obj         return out

User · Answer

The lodash 4 6 1 docs have this as an example for object key equality     uniqWith objects    isEqual    https   lodash com docs uniqWith

[javascript] Removing duplicate objects with Underscore for Javascript

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