Count the number of occurrences of a character in a string in Javascript

Question

I need to count the number of occurrences of a character in a string   For example  suppose my string contains   var mainStr    str1 str2 str3 str4     I want to find the count of comma   character  which is 3  And the count of individual strings after the split along comma  which is 4   I also need to validate that each of the strings i e str1 or str2 or str3 or str4 should not exceed  say  15 characters

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Simply  use the split to find out the number of occurrences of a character in a string   mainStr split      length    gives 4 which is the number of strings after splitting using delimiter comma mainStr split      length - 1    gives 3 which is the count of comma

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This below is the simplest logic  which is very easy to understand      Demo string with repeat char    let str    Coffee      Splitted the str into an char array for looping   let strArr   str split         This below is the final object which holds the result   let obj           This loop will count char  You can also use traditional one for loop    strArr forEach  value index   gt           If the char exists in the object it will simple increase its value       if obj value     undefined                    obj value    parseInt obj value     1           else it will add the new one with initializing 1       else            obj value   1                         console log  Char with Count   JSON stringify obj      Char with Count   C  1  o  1  f  2  e  2

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Here is a similar solution  but it uses Array prototype reduce   function countCharacters char  string      return string split     reduce  acc  ch    gt  ch     char   acc   1  acc  0      As was mentioned  String prototype split works much faster than String prototype replace

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x000D   x000D  var i   0  x000D   x000D  var split start   new Date   getTime    x000D  while  i  lt  30000    x000D     1234 453 123 324  split      length -1  x000D    i    x000D    x000D  var split end   new Date   getTime    x000D  var split time   split end - split start  x000D   x000D   x000D  i  0  x000D  var reg start   new Date   getTime    x000D  while  i  lt  30000    x000D      1234 453 123 324  match    g         length  x000D    i    x000D    x000D  var reg end   new Date   getTime    x000D  var reg time   reg end - reg start  x000D   x000D  alert   Split Execution time      split time     n     RegExp Execution time      reg time     n    x000D   x000D   x000D

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ok  an other one with regexp - probably not fast  but short and better readable then others  in my case just     to count  key replace       g     length   just remove everything that does not look like your char  but it does not look nice with a string as input

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What about string split desiredCharecter  length-1  Example   var str    hellow how is life   var len   str split  h   length-1  will give count 2 for character  h  in the above string

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s    dir dir dir dir   for i l 0 i lt s length i    if s i          l

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Add this function to sting prototype    String prototype count function c       var result   0  i   0    for i i lt this length i   if this i   c result      return result       usage   console log  strings  count  s       2

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I know this might be an old question but I have a simple solution for low-level beginners in JavaScript    As a beginner  I could only understand some of the solutions to this question so I used two nested FOR loops to check each character against every other character in the string  incrementing a count variable for each character found that equals that character   I created a new blank object where each property key is a character and the value is how many times each character appeared in the string count    Example function -  function countAllCharacters str      var obj         if str length   0       for i 0 i lt str length i           var count   0        for j 0 j lt str length j             if str i      str j              count                            if  obj hasOwnProperty str i             obj str i     count                      return obj

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Here s one just as fast as the split   and the replace methods  which are a tiny bit faster than the regex method  in Chrome and Firefox both    let num   0  let str    str1 str2 str3 str4     Note  Pre-calculating   length  is an optimization    otherwise  it recalculates it every loop iteration  let len   str length    Note  Don t use a  for      of       loop  it s slow  for  let charIndex   0  charIndex  lt  len    charIndex      if  str charIndex                   num

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I just did a very quick and dirty test on repl it using Node v7 4  For a single character  the standard for loop is quickest  Some code     winner  function charCount1 s  c        let count   0      c   c charAt 0      we save some time here     for let i   0  i  lt  s length    i            if c     s charAt i                   count                      return count     function charCount2 s  c        return  s match new RegExp c 0    g           length     function charCount3 s  c        let count   0      for ch of s            if c     ch                  count                      return count     function perfIt         const s    Hello  World        const c    o        console time  charCount1        for let i   0  i  lt  10000  i              charCount1 s  c             console timeEnd  charCount1             console time  charCount2        for let i   0  i  lt  10000  i              charCount2 s  c             console timeEnd  charCount2             console time  charCount3        for let i   0  i  lt  10000  i              charCount2 s  c             console timeEnd  charCount3       Results from a few runs  perfIt   charCount1  3 301ms charCount2  11 652ms charCount3  174 043ms undefined  perfIt   charCount1  2 110ms charCount2  11 931ms charCount3  177 743ms undefined  perfIt   charCount1  2 074ms charCount2  11 738ms charCount3  152 611ms undefined  perfIt   charCount1  2 076ms charCount2  11 685ms charCount3  154 757ms undefined  Update 2021-Feb-10  Fixed typo in repl it demo Update 2020-Oct-24  Still the case with Node js 12  play with it yourself here

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I was working on a small project that required a sub-string counter  Searching for the wrong phrases provided me with no results  however after writing my own implementation I have stumbled upon this question  Anyway  here is my way  it is probably slower than most here but might be helpful to someone   function count letters     var counter   0   for  var i   0  i  lt  input length  i          var index of sub   input indexOf input letter  i        if  index of sub  gt  -1            counter            i   index of sub            http   jsfiddle net 5ZzHt 1   Please let me know if you find this implementation to fail or do not follow some standards      UPDATE You may want to substitute       for  var i   0  i  lt  input length  i        With   for  var i   0  input length   input length  i  lt  input length  i        Interesting read discussing the above  http   www erichynds com blog javascript-length-property-is-a-stored-value

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I have found that the best approach to search for a character in a very large string  that is 1 000 000 characters long  for example  is to use the replace   method   window count replace   function  str  schar        return str length - str replace RegExp schar       length       You can see yet another JSPerf suite to test this method along with other methods of finding a character in a string

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And there is   function character count string  char  ptr   0  count   0        while  ptr   string indexOf char  ptr    1   count         return count     Works with integers too

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x000D   x000D  var mainStr    str1 str2 str3 str4   var splitStr   mainStr split      length alert splitStr  x000D   x000D   x000D

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A quick Google search got this  from http   www codecodex com wiki index php title Count the number of occurrences of a specific character in a string JavaScript   String prototype count function s1         return  this length - this replace new RegExp s1  g        length    s1 length      Use it like this   test    one two three four  commas   test count         returns 3

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Here is my solution  Lots of solution already posted before me  But I love to share my view here   const mainStr    str1 str2 str3 str4    const commaAndStringCounter    str    gt      const commas       str  filter letter   gt  letter          length    const numOfStr   str split      length     return  Commas    commas   String    numOfStr          Run the code console log commaAndStringCounter mainStr       Output  Commas  3  String  4   Here you find my REPL

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Performance of Split vs RegExp   x000D   x000D  var i   0  x000D   x000D  var split start   new Date   getTime    x000D  while  i  lt  30000    x000D     1234 453 123 324  split      length -1  x000D    i    x000D    x000D  var split end   new Date   getTime    x000D  var split time   split end - split start  x000D   x000D   x000D  i  0  x000D  var reg start   new Date   getTime    x000D  while  i  lt  30000    x000D      1234 453 123 324  match    g         length  x000D    i    x000D    x000D  var reg end   new Date   getTime    x000D  var reg time   reg end - reg start  x000D   x000D  alert   Split Execution time      split time     n     RegExp Execution time      reg time     n    x000D   x000D   x000D

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The fastest method seems to be via the index operator    x000D   x000D  function charOccurances  str  char  x000D    x000D    for  var c   0  i   0  len   str length  i  lt  len    i  x000D      x000D      if  str i     char  x000D        x000D          c  x000D        x000D      x000D    return c  x000D    x000D   x000D  console log  charOccurances  example path script js              2 x000D   x000D   x000D    Or as a prototype function    x000D   x000D  String prototype charOccurances   function  char  x000D    x000D    for  var c   0  i   0  len   this length  i  lt  len    i  x000D      x000D      if  this i     char  x000D        x000D          c  x000D        x000D      x000D    return c  x000D    x000D   x000D  console log   example path script js  charOccurances            2 x000D   x000D   x000D

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I have updated this answer  I like the idea of using a match better  but it is slower   console log   str1 str2 str3 str4  match    g         length     logs 3  console log   str1 str2 str3 str4  match new RegExp  str    g           length     logs 4   jsfiddle  Use a regular expression literal if you know what you are searching for beforehand  if not you can use the RegExp constructor  and pass in the g flag as an argument   match returns null with no results thus the        The original answer I made in 2009 is below  It creates an array unnecessarily  but using a split is faster  as of September 2014   I m ambivalent  if I really needed the speed there would be no question that I would use a split  but I would prefer to use match   Old answer  from 2009    If you re looking for the commas    mainStr split      length - 1    3   If you re looking for the str   mainStr split  str   length - 1    4   Both in  Lo s answer and in my own silly jsperf test split comes ahead in speed  at least in Chrome  but again creating the extra array just doesn t seem sane

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There are at least four ways  The best option  which should also be the fastest -owing to the native RegEx engine -  is placed at the top  jsperf com is currently down  otherwise I would provide you with performance statistics  Update  Please  find the performance tests here  and run them yourselves  so as to contribute your performance results  The specifics of the results will be given later  1     quot this is foo bar quot  match  o g       length     gt 2  2   quot this is foo bar quot  split  quot o quot   length-1     gt 2  split not recommended  Resource hungry  Allocates new instances of  Array  for each match  Don t try that for a  gt 100MB file via FileReader  You can actually easily observe the EXACT resource usage using Chrome s profiler option  3  var stringsearch    quot o quot      str    quot this is foo bar quot   for var count -1 index -2  index    -1  count   index str indexOf stringsearch index 1         gt count 2  4  searching for a single character var stringsearch    quot o quot      str    quot this is foo bar quot   for var i count 0  i lt str length  count    stringsearch   str i           gt count 2  Update  5  element mapping and filtering  not recommended due to its overall resource preallocation rather than using Pythonian  generators  var str    quot this is foo bar quot  str split     map  function e i   if e      o   return i                   filter Boolean     gt  9  10   9  10  length    gt 2  Share  I made this gist  with currently 8 methods of character-counting  so we can directly pool and share our ideas - just for fun  and perhaps some interesting benchmarks    https   gist github com 2757250

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My solution   function countOcurrences str  value      var regExp   new RegExp value   gi       return str match regExp    str match regExp  length   0

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The function takes string str as parameter and counts occurrence of each unique characters in the string  The result comes in key - value pair for each character    var charFoundMap        object defined     for  var i   0  i  lt  str length  i              if  charFoundMap  str i                charFoundMap  str i    1                   else        charFoundMap  str i      1           if object does not contain this            return charFoundMap

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let str    quot aabgrhaab quot  let charMap       for let char of text       if charMap hasOwnProperty char          charMap char         else        charMap char    1         console log charMap      a  4  b  2  g  1  r  1  h  1

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I believe you will find the below solution to be very short  very fast  able to work with very long strings  able to support multiple character searches  error proof  and able to handle empty string searches   function substring count source str  search str  index        source str        search str            var count   -1  index inc   Math max search str length  1       index     index    0  - index inc      do             count          index   source str indexOf search str  index   index inc         while   index       return count      Example usage    x000D   x000D  console log substring count  Lorem ipsum dolar un sit amet     m     x000D   x000D  function substring count source str  search str  index    x000D      source str        search str        x000D      var count   -1  index inc   Math max search str length  1   x000D      index     index    0  - index inc  x000D      do   x000D            count  x000D          index   source str indexOf search str  index   index inc   x000D        while   index   x000D      return count  x000D    x000D   x000D   x000D    The above code fixes the major performance bug in Jakub Wawszczyk s that the code keeps on looks for a match even after indexOf says there is none and his version itself is not working because he forgot to give the function input parameters

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Easiest way i found out     Example-  str    mississippi    function find occurences str  char to count       return str split char to count  length - 1     find occurences str   i     outputs 4

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The fifth method in Leo Sauers answer fails  if the character is on the beginning of the string  e g    var needle   A     haystack    AbcAbcAbc    haystack split     map  function e i   if e     needle  return i        filter Boolean  length    will give 2 instead of 3  because the filter funtion Boolean gives false for 0   Other possible filter function   haystack split     map function  e  i      if  e     needle  return i     filter function  item      return  isNaN item      length

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The following uses a regular expression to test the length  testex ensures you don t have 16 or greater consecutive non-comma characters  If it passes the test  then it proceeds to split the string  counting the commas is as simple as counting the tokens minus one   var mainStr    str1 str2 str3 str4   var testregex          16    g  if  testregex test mainStr       alert  values must be separated by commas and each may not exceed 15 characters      else     var strs   mainStr split         alert  mainStr contains     strs length     substrings separated by commas       alert  mainStr contains      strs length-1      commas

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My solution with ramda js   const testString    somestringtotest   const countLetters   R compose    R map R length     R groupBy R identity     R split        countLetters testString    Link to REPL

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I m using Node js v 6 0 0 and the fastest is the one with index  the 3rd method in Lo Sauer s answer    The second is    x000D   x000D  function count s  c    x000D    var n   0  x000D    for  let x of s    x000D      if  x    c  x000D        n    x000D      x000D    return n  x000D    x000D   x000D   x000D

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If you are using lodash  the   countBy method will do this     countBy  abcda    a     2   This method also work with array     countBy   ab    cd    ab     ab     2

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I made a slight improvement on the accepted answer  it allows to check with case-sensitive case-insensitive matching  and is a method attached to the string object   String prototype count   function lit  cis        var m   this toString   match new RegExp lit    cis     gi     g          return  m    null    m length   0      lit is the string to search for   such as  ex     and cis is case-insensitivity  defaulted to false  it will allow for choice of case insensitive matches   To search the string  I love StackOverflow com  for the lower-case letter  o   you would use   var amount of os    I love StackOverflow com  count  o      amount of os would be equal to 2   If we were to search the same string again using case-insensitive matching  you would use   var amount of os    I love StackOverflow com  count  o   true     This time  amount of os would be equal to 3  since the capital O from the string gets included in the search

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var a    acvbasbb   var b      for  let i 0 i lt a length i         if  a match new RegExp a i    g     length  gt  1           b a i    a match new RegExp a i    g     length          console log b     In javascript you can use above code to get occurrence of a character in a string

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You can also rest your string and work with it like an array of elements using   Array prototype filter      x000D   x000D  const mainStr    str1 str2 str3 str4   x000D  const commas       mainStr  filter l   gt  l          length  x000D   x000D  console log commas   x000D   x000D   x000D    Or    Array prototype reduce      x000D   x000D  const mainStr    str1 str2 str3 str4   x000D  const commas       mainStr  reduce  a  c    gt  c             a   a  0   x000D   x000D  console log commas   x000D   x000D   x000D

[javascript] Count the number of occurrences of a character in a string in Javascript

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