Check if an array contains duplicate values

Question

I wanted to write a javascript function which checks if array contains duplicate values or not   I have written the following code but its giving answer as  true  always   Can anybody please tell me what am I missing   function checkIfArrayIsUnique myArray                 for  var i   0  i  lt  myArray length  i                           for  var j   0  j  lt  myArray length  j                                   if  i    j                                         if  myArray i     myArray j                                                  return true     means there are duplicate values                                                                         return false     means there are no duplicate values

User · Answer

Late answer but can be helpful   function areThereDuplicates args         let count           for let i   0  i  lt  args length  i              count args i     1    count args i      0             let found   Object keys count  filter function key            return count key   gt  1              return found length   true   false      areThereDuplicates  1 2 5

User · Answer

You got the return values the wrong way round    As soon as you find two values that are equal  you can conclude that the array is not unique and return false  At the very end  after you ve checked all the pairs  you can return true    If you do this a lot  and the arrays are large  you might want to investigate the possibility of sorting the array and then only comparing adjacent elements  This will have better asymptotic complexity than your current method

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Returns the duplicate item in array and creates a new array with no duplicates    var a     hello    hi    hi    juice    juice    test        var b     ding    dong    hi    juice    juice    test        var c   a concat b       var dupClearArr            function dupArray arr             for  i   0  i  lt  arr length  i                  if  arr indexOf arr i      i  amp  amp  arr indexOf arr i      -1                    console log  duplicate item     arr i                  else                   dupClearArr push arr i                                    console log  actual array  n    arr      nno duplicate items array  n    dupClearArr             dupArray c

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function hasNoDuplicates arr        return arr every num   gt  arr indexOf num      arr lastIndexOf num       hasNoDuplicates accepts an array and returns true if there are no duplicate values  If there are any duplicates  the function returns false

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function checkIfArrayIsUnique myArray               isUnique true          for  var i   0  i  lt  myArray length  i                           for  var j   0  j  lt  myArray length  j                                   if  i    j                                         if  myArray i     myArray j                                                  isUnique false                                                                         return isUnique          This assume that the array is unique at the start   If find two equals values  then change to false

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Assuming you re targeting browsers that aren t IE8   this would work as well   function checkIfArrayIsUnique myArray         for  var i   0  i  lt  myArray length  i                   if  myArray indexOf myArray i       myArray lastIndexOf myArray i                   return false                         return true       this means not unique

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The best solution ever    Array prototype checkIfArrayIsUnique   function         this sort            for   var i   1  i  lt  this length  i              if this i-1     this i               return false            return true

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Wrote this to initialize a new array of length uniqueIndexCount  It s presented here minus unrelated logic       public Vector3   StandardizeVertices Vector3   dimensions  int standard                  determine the number of unique dimension vectors         int uniqueIndexCount   0          for  int a 0  a  lt  dimensions Length    a                        int duplicateIndexCount   0              for  int b   a  b  lt  dimensions Length    b                                if a  b  amp  amp  dimensions a     dimensions b                                         duplicateIndexCount                                                if  duplicateIndexCount    0                                uniqueIndexCount                                    Debug Log  uniqueIndexCount    uniqueIndexCount           return dimensions

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Here s an O n  solution   function hasDupes arr         temporary object      var uniqOb            create object attribute with name value in array  this will not keep dupes     for  var i in arr      uniqOb arr i              if object s attributes match array  then no dupes       if  arr length    Object keys uniqOb  length      alert  NO dupes      else     alert  HAS dupes        var arr     1 1 2016    1 1 2016    2 1 2016    hasDupes arr     https   jsfiddle net 7kkgy1j3

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An easy solution  if you ve got ES6  uses Set    x000D   x000D  function checkIfArrayIsUnique myArray    x000D    return myArray length     new Set myArray  size  x000D    x000D   x000D  let uniqueArray    1  2  3  4  5   x000D  console log    uniqueArray  is unique     checkIfArrayIsUnique uniqueArray      x000D   x000D  let nonUniqueArray    1  1  2  3  4  5   x000D  console log    nonUniqueArray  is unique     checkIfArrayIsUnique nonUniqueArray      x000D   x000D   x000D

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let arr    11 22 11 22    let hasDuplicate   arr some  val  i    gt  arr indexOf val      i      hasDuplicate   true      True -  array has duplicates      False -  uniqe array

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This should work with only one loop   function checkIfArrayIsUnique arr        var map       i  size       for  i   0  size   arr length  i  lt  size  i             if  map arr i                 return false                     map arr i     true             return true

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Without a for loop  only using Map     You can also return the duplicates    function a     let map   new Map       a forEach e   gt        if map has e           let count   map get e         console log count        map set e  count   1         else         map set e  1                  let hasDup   false    let dups         map forEach  value  key    gt        if value  gt  1          hasDup   true        dups push key                  console log dups      return hasDup       2 4 6 2 1 4

User · Answer

The code given in the question can be better written as follows  function checkIfArrayIsUnique myArray                 for  var i   0  i  lt  myArray length  i                           for  var j   i 1  j  lt  myArray length  j                                                         if  myArray i     myArray j                                                  return true     means there are duplicate values                                                        return false     means there are no duplicate values

[javascript] Check if an array contains duplicate values

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