How can I check if the array of objects have duplicate property values

Question

I need some help with iterating through array  I keep getting stuck or reinventing the wheel   values           name   someName1           name   someName2           name   someName1           name   someName1        How could I check if there are two  or more  same name value in array  I do not need a counter  just setting some variable if array values are not unique  Have in mind that array length is dynamic  also array values

User · Answer

Try an simple loop   var repeat       tmp  i   0   while i  lt  values length     repeat indexOf tmp   values i    name   gt  -1   values pop i--    repeat push tmp      Demo

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ECMA Script 6 Version  If you are in an environment which supports ECMA Script 6 s Set  then you can use Array prototype some and a Set object  like this  let seen   new Set    var hasDuplicates   values some function currentObject        return seen size     seen add currentObject name  size        Here  we insert each and every object s name into the Set and we check if the size before and after adding are the same  This works because Set size returns a number based on unique data  set only adds entries if the data is unique   If when you have duplicate names  the size won t increase  because the data won t be unique  which means that we would have already seen the current name and it will return true     ECMA Script 5 Version  If you don t have Set support  then you can use a normal JavaScript object itself  like this  var seen       var hasDuplicates   values some function currentObject         if  seen hasOwnProperty currentObject name                Current name is already seen         return true                Current name is being seen for the first time     return  seen currentObject name    false         The same can be written succinctly  like this  var seen       var hasDuplicates   values some function  currentObject        return seen hasOwnProperty currentObject name              seen currentObject name    false           Note  In both the cases  we use Array prototype some because it will short-circuit  The moment it gets a truthy value from the function  it will return true immediately  it will not process rest of the elements

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checking duplicate elements in an array var arr  1 3 4 6 8 9 1 3 4 7   var hp new Map    console log arr sort     var freq 0  for var i 1 i lt arr length i        console log arr i-1      arr i    if arr i   arr i-1    freq       else  hp set arr i-1  freq 1   freq 0      console log hp

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In TS and ES6 you can create a new Set with the property to be unique and compare it s size to the original array    x000D   x000D  const values     x000D      name   someName1     x000D      name   someName2     x000D      name   someName3     x000D      name   someName1    x000D    x000D   x000D  const uniqueValues   new Set values map v   gt  v name    x000D   x000D  if  uniqueValues size  lt  values length    x000D    console log  duplicates found   x000D    x000D   x000D   x000D

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Use array prototype map and array prototype some   var values           name   someName1           name   someName2           name   someName4           name   someName2        var valueArr   values map function item   return item name     var isDuplicate   valueArr some function item  idx        return valueArr indexOf item     idx      console log isDuplicate     JSFIDDLE

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With Underscore js A few ways with Underscore can be done  Here is one of them  Checking if the array is already unique   function isNameUnique values       return   uniq values  function v   return v name    length    values length     With vanilla JavaScript  By checking if there is no recurring names in the array   function isNameUnique values       var names   values map function v   return v name         return  names some function v            return names filter function w   return w  v    length gt 1

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To know if simple array has duplicates we can compare first and last indexes of the  same value    The function   var hasDupsSimple   function array         return array some function value                                   some will break as soon as duplicate found  no need to itterate over all array         return array indexOf value      array lastIndexOf value        comparing first and last indexes of the same value            Tests   hasDupsSimple  1 2 3 4 2 7        gt  true  hasDupsSimple  1 2 3 4 8 7        gt  false  hasDupsSimple  1  hello  3  bye   hello  7        gt  true      For an array of objects we need to convert the objects values to a simple array first    Converting array of objects to the simple array with map   var hasDupsObjects   function array       return array map function value        return value suit   value rank       some function value  index  array            return array indexOf value      array lastIndexOf value                 Tests   var cardHand          suit   spades    rank   ten          suit   diamonds    rank   ace          suit   hearts    rank   ten          suit   clubs    rank   two          suit   spades    rank   three        hasDupsObjects cardHand        gt  false     var cardHand2          suit   spades    rank   ten          suit   diamonds    rank   ace          suit   hearts    rank   ten          suit   clubs    rank   two          suit   spades    rank   ten        hasDupsObjects cardHand2        gt  true

User · Answer

if you are looking for a boolean  the quickest way would be    x000D   x000D  var values     x000D        name   someName1     x000D        name   someName2     x000D        name   someName1     x000D        name   someName1    x000D    x000D   x000D     solution x000D  var hasDuplicate   false  x000D  values map v   gt  v name  sort   sort  a  b    gt    x000D    if  a     b  hasDuplicate   true x000D     x000D  console log  hasDuplicate   hasDuplicate  x000D   x000D   x000D

User · Answer

You can use map to return just the name  and then use this forEach trick to check if it exists at least twice   var areAnyDuplicates   false   values map function obj        return obj name     forEach function  element  index  arr        if  arr indexOf element      index            areAnyDuplicates   true              Fiddle

[javascript] How can I check if the array of objects have duplicate property values?

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