How to count duplicate value in an array in javascript

Question

Currently  I got an array like that   var uniqueCount   Array      After a few steps  my array looks like that   uniqueCount    a b c d d e a b c f g h h h e a     How can I count how many a b c are there in the array  I want to have a result like   a   3 b   1 c   2 d   2   etc

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You can have an object that contains counts   Walk over the list and increment the count for each element   var counts        uniqueCount forEach function element      counts element     counts element     0    1       for  var element in counts      console log element           counts element

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Count the Letters provided in string function countTheElements             var str    quot ssdefrcgfrdesxfdrgs quot       var arr           var count   0           for var i 0 i lt str length i             arr push str i                           arr sort        for var i 0 i lt arr length i                  if arr i     arr i-1                count             else                      count   1                                if arr i     arr i 1                    console log arr i    quot    quot   count                                                          countTheElements

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uniqueCount     a   b   a   c   b   a   d   b   c   f   g   h   h   h   e   a    var count       uniqueCount forEach  i    gt    count i      count i    1    console log count

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Nobody responding seems to be using the Map   built-in for this  which tends to be my go-to combined with Array prototype reduce      x000D   x000D  const data     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a    x000D  const result   data reduce  a  c    gt  a set c   a get c     0    1   new Map     x000D  console log    result   x000D   x000D   x000D    N b   you ll have to polyfill Map   if wanting to use it in older browsers

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x000D   x000D  var string     a   a   b   c   c   c   c   c   a   a   a    x000D   x000D  function stringCompress string   x000D   x000D  var obj      str       x000D  string forEach function i     x000D    obj i     obj i   0    1  x000D      x000D   x000D  for var key in obj   x000D    str     key obj key    x000D    x000D    console log obj   x000D    console log str   x000D   stringCompress string  x000D   x000D     x000D  Always open to improvement  please share  x000D     x000D   x000D   x000D

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simplified sheet js answare   x000D   x000D  var counts       x000D  var aarr   a   b   a    x000D  aarr forEach x  gt counts x   counts x     0  1    x000D  console log counts  x000D   x000D   x000D

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x000D   x000D  function count     x000D      array elements     a    b    c    d    e    a    b    c    f    g    h    h    h    e    a    x000D   x000D      array elements sort    x000D   x000D      var current   null  x000D      var cnt   0  x000D      for  var i   0  i  lt  array elements length  i      x000D          if  array elements i     current    x000D              if  cnt  gt  0    x000D                  document write current     comes -- gt      cnt     times lt br gt     x000D                x000D              current   array elements i   x000D              cnt   1  x000D            else   x000D              cnt    x000D            x000D        x000D      if  cnt  gt  0    x000D          document write current     comes -- gt      cnt     times    x000D        x000D   x000D    x000D   x000D  count    x000D   x000D   x000D     Demo Fiddle  You can use higher-order functions too to do the operation  See this answer

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Duplicates in an array containing alphabets    x000D   x000D  var arr     a    b    a    z    e    a    b    f    d    f    x000D    sortedArr       x000D    count   1  x000D   x000D  sortedArr   arr sort    x000D   x000D  for  var i   0  i  lt  sortedArr length  i   i   count    x000D    count   1  x000D    for  var j   i   1  j  lt  sortedArr length  j      x000D      if  sortedArr i      sortedArr j   x000D        count    x000D      x000D    document write sortedArr i            count     lt br gt     x000D    x000D   x000D   x000D    Duplicates in an array containing numbers    x000D   x000D  var arr    2  1  3  2  8  9  1  3  1  1  1  2  24  25  67  10  54  2  1  9  8  1   x000D    sortedArr       x000D    count   1  x000D  sortedArr   arr sort function a  b    x000D    return a - b x000D      x000D  for  var i   0  i  lt  sortedArr length  i   i   count    x000D    count   1  x000D    for  var j   i   1  j  lt  sortedArr length  j      x000D      if  sortedArr i      sortedArr j   x000D        count    x000D      x000D    document write sortedArr i            count     lt br gt     x000D    x000D   x000D   x000D

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Declare an object arr to hold the unique set as keys  Populate arr by looping through the array once using map  If the key has not been previously found then add the key and assign a value of zero  On each iteration increment the key s value    Given testArray   var testArray     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a      solution   var arr       testArray map x  gt   if typeof arr x     undefined   arr x  0  arr x          JSON stringify arr  will output    a  3  b  2  c  2  d  2  e  2  f  1  g  1  h  3    Object keys arr  will return   a   b   c   d   e   f   g   h    To find the occurrences of any item e g  b arr  b   will output 2

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Create a file for example demo js and run it in console with node demo js and you will get occurrence of elements in the form of matrix   var multipleDuplicateArr   Array 10  fill 0  map     gt  return Math floor Math random     Math floor 9      console log multipleDuplicateArr    var resultArr   Array Array  KEYS   OCCURRENCE      for  var i   0  i  lt  multipleDuplicateArr length  i        var flag   true    for  var j   0  j  lt  resultArr length  j           if resultArr j  0     multipleDuplicateArr i           resultArr j  1    resultArr j  1    1         flag   false                if flag       resultArr push Array multipleDuplicateArr i  1           console log resultArr     You will get result in console as below      1  4  5  2  6  8  7  5  0  5        multipleDuplicateArr      KEYS    OCCURENCE               resultArr     1  1        4  1        5  3        2  1        6  1        8  1        7  1        0  1

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It is simple in javascript using array reduce method   x000D   x000D  const arr     a   d   r   a   a   f   d    const result    arr reduce  json val   gt      json   val   json val    0    1        console log result      a 3 d 2 r 1 f 1   x000D   x000D   x000D

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I think this is the simplest way how to count occurrences with same value in array   var a    true  false  false  false   a filter function value       return value     false     length

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Something like this    x000D   x000D  uniqueCount     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a    x000D  var count       x000D  uniqueCount forEach function i    count i     count i   0    1     x000D  console log count   x000D   x000D   x000D    Use a simple for loop instead of forEach if you don t want this to break in older browsers

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var uniqueCount     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a       here we will collect only unique items from the array var uniqueChars           iterate through each item of uniqueCount for  i of uniqueCount       if this is an item that was not earlier in uniqueCount      put it into the uniqueChars array   if  uniqueChars indexOf i     -1        uniqueChars push i             after iterating through all uniqueCount take each item in uniqueChars    and compare it with each item in uniqueCount  If this uniqueChars item     corresponds to an item in uniqueCount  increase letterAccumulator by one  for  x of uniqueChars      let letterAccumulator   0    for  i of uniqueCount        if  i    x   letterAccumulator           console log    x      letterAccumulator

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You can solve it without using any for while loops ou forEach   function myCounter inputWords                return inputWords reduce   countWords  word    gt            countWords word      countWords word     1          return countWords                  Hope it helps you

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By using array map we can reduce the loop  see this on jsfiddle  function Check        var arr   Array prototype slice call arguments       var result           for i 0  i lt  arr length  i             var duplicate   0          var val   arr i           arr map function x               if val     x  duplicate                       result push duplicate gt   2             return result      To Test   var test   new Check 1 2 1 4 1   console log test

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CODE  function getUniqueDataCount objArr  propName            var data               objArr forEach function  d  index                if  d propName                     data push d propName                                       var uniqueList       new Set data             var dataSet               for  var i 0  i  lt  uniqueList length  i                  dataSet uniqueList i     data filter x   gt  x    uniqueList i   length                             return dataSet         Snippet  x000D   x000D  var data               a  you  b  b  c  c  d  c               a   you   b   b   c   c   d  c               a   them   b   b   c   c   d  c               a   them   b   b   c   c   d  c               a   okay   b   b   c   c   d  c               a   okay   b   b   c   c   d  c                              console log getUniqueDataCount data   a                 function getUniqueDataCount objArr  propName            var data               objArr forEach function  d  index                if  d propName                     data push d propName                                       var uniqueList       new Set data             var dataSet               for  var i 0  i  lt  uniqueList length  i                  dataSet uniqueList i     data filter x   gt  x    uniqueList i   length                     return dataSet        x000D   x000D   x000D

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var testArray     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a     var newArr       testArray forEach  item    gt        newArr item    testArray filter  el    gt                return el     item         length     console log newArr

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Quickest way    omputational complexity is O n     x000D   x000D  function howMuchIsRepeated es5 arr    x000D   const count       x000D   for  let i   0  i  lt  arr length  i      x000D    const val   arr i   x000D    if  val in count    x000D     count val    count val    1  x000D      else   x000D     count val    1  x000D      x000D     x000D   x000D   for  let key in count    x000D    console log  Value     key     is repeated     count key      times    x000D     x000D    x000D   x000D  howMuchIsRepeated es5   a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a     x000D   x000D   x000D    The shortest code   Use ES6    x000D   x000D  function howMuchIsRepeated es6 arr    x000D      count is    valX  count    valY  count    valZ  count        x000D   const count       new Set arr   map val   gt   val  arr join     split val  length - 1    x000D   x000D   for  let i   0  i  lt  count length  i      x000D    console log  Value   count i  0   is repeated   count i  1   times    x000D     x000D    x000D   x000D  howMuchIsRepeated es6   a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a     x000D   x000D   x000D

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Initial array let array     a    b    c    d    d    e    a    b    c    f    g    h    h    h    e    a        Unique array without duplicates   a    b          h   let unique       new Set array        This array counts duplicates    a   3     b   2           h   3    let duplicates   unique map value   gt   value  array filter str   gt  str     value  length

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var arr     a   d   r   a   a   f   d         call function and pass your array  function will return an object with array values as keys and their count as the key values  duplicatesArr arr    function duplicatesArr arr       var obj          for var i   0  i  lt  arr length  i             obj arr i                 for var x   0  x  lt  arr length  x                  arr i     arr x     obj arr i   push x                          obj arr i     obj arr i   length             console log obj       return obj

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let arr  1 2 3 3 4 5 5 6 7 7  let obj    for var i 0 i lt arr length i         obj arr i   obj arr i    null  obj arr i   1 1   stores duplicate in an obj    console log obj    returns object  1 1  1 3 2

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x000D   x000D     new example  x000D  var str   20 1 -1 2 -2 3 3 5 5 1 2 4 20 4 -1 -2 5   x000D   x000D  function findOdd para    x000D    var count       x000D    para forEach function para    x000D    count para     count para     0    1  x000D        x000D    return count  x000D    x000D   x000D  console log findOdd str    x000D   x000D   x000D

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A combination of good answers     var count       var arr     a    b    c    d    d    e    a    b    c    f    g    h    h    h    e    a    var iterator   function  element        count element     count element     0    1     if  arr forEach        arr forEach function  element            iterator element             else       for  var i   0  i  lt  arr length  i              iterator arr i                Hope it s helpful

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var counts       your array forEach function x    counts x     counts x     0  1

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public class CalculateCount   public static void main String   args        int a      1 2 1 1 5 4 3 2 2 1 4 4 5 3 4 5 4       Arrays sort a       int count 1      int i      for i 0 i lt a length-1 i             if a i   a i 1                System out println  The Number   a i    appears   count   times                count 1                                    else              count                        System out println  The Number   a i    appears   count   times

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I stumbled across this  very old  question  Interestingly the most obvious and elegant solution  imho  is missing  Array prototype reduce       All major browsers support this feature since about 2011  IE  or even earlier  all others     x000D   x000D  var arr     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a    x000D  var map   arr reduce function prev  cur    x000D    prev cur     prev cur     0    1  x000D    return prev  x000D          x000D   x000D     map is an associative array mapping the elements to their frequency  x000D  document write JSON stringify map    x000D     prints   a   3   b   2   c   2   d   2   e   2   f   1   g   1   h   3  x000D   x000D   x000D

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Single line based on reduce array function  x000D   x000D  const uniqueCount      a    b    c    d    d    e    a    b    c    f    g    h    h    h    e    a    const distribution   uniqueCount reduce  acum cur    gt  Object assign acum   cur    acum cur     0  1        console log JSON stringify distribution null 2    x000D   x000D   x000D

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Simple is better  one variable  one function     const counts   arr reduce  acc  value    gt           acc      value    acc value     0    1

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You can do something like that   uniqueCount     a   b   c   d   d   e   a   b   c   f   g   h   h   h   e   a    var map   new Object     for var i   0  i  lt  uniqueCount length  i       if map uniqueCount i      null        map uniqueCount i      1    else       map uniqueCount i     1            now you have a map with all characters count

[javascript] How to count duplicate value in an array in javascript

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