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

The Question :

581 people think this question is useful

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.

The Question Comments :

The Answer 1

840 people think this answer is useful

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.

The Answer 2

237 people think this answer is useful

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.

 ("this is foo bar".match(/o/g)||[]).length
 //>2

2.

"this is foo bar".split("o").length-1
 //>2

split not recommended. Resource hungry. Allocates new instances of ‘Array’ for each match. Don’t try that for a >100MB file via FileReader. You can actually easily observe the EXACT resource usage using Chrome’s profiler option.

3.

var stringsearch = "o"
   ,str = "this is foo bar";
for(var count=-1,index=-2; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
 //>count:2

4.

searching for a single character

var stringsearch = "o"
   ,str = "this is foo bar";
for(var i=count=0; i<str.length; count+=+(stringsearch===str[i++]));
 //>count:2

Update:

5.

element mapping and filtering, not recommended due to its overall resource preallocation rather than using Pythonian ‘generators’

var str = "this is foo bar"
str.split('').map( function(e,i){ if(e === 'o') return i;} )
             .filter(Boolean)
//>[9, 10]
[9, 10].length
//>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

The Answer 3

20 people think this answer is useful

Add this function to sting prototype :

String.prototype.count=function(c) { 
  var result = 0, i = 0;
  for(i;i<this.length;i++)if(this[i]==c)result++;
  return result;
};

usage:

console.log("strings".count("s")); //2

The Answer 4

13 people think this answer is useful

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

The Answer 5

12 people think this answer is useful

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

The Answer 6

9 people think this answer is useful

Here is a similar solution, but it uses Array.prototype.reduce

function countCharacters(char, string) {
  return string.split('').reduce((acc, ch) => ch === char ? acc + 1: acc, 0)
}

As was mentioned, String.prototype.split works much faster than String.prototype.replace.

The Answer 7

8 people think this answer is useful

You can also rest your string and work with it like an array of elements using

const mainStr = 'str1,str2,str3,str4';
const commas = [...mainStr].filter(l => l === ',').length;

console.log(commas);

Or

const mainStr = 'str1,str2,str3,str4';
const commas = [...mainStr].reduce((a, c) => c === ',' ? ++a : a, 0);

console.log(commas);

The Answer 8

6 people think this answer is useful

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.

The Answer 9

5 people think this answer is useful

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

The Answer 10

4 people think this answer is useful

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.

The Answer 11

4 people think this answer is useful

Performance of Split vs RegExp

var i = 0;

var split_start = new Date().getTime();
while (i < 30000) {
  "1234,453,123,324".split(",").length -1;
  i++;
}
var split_end = new Date().getTime();
var split_time = split_end - split_start;


i= 0;
var reg_start = new Date().getTime();
while (i < 30000) {
  ("1234,453,123,324".match(/,/g) || []).length;
  i++;
}
var reg_end = new Date().getTime();
var reg_time = reg_end - reg_start;

alert ('Split Execution time: ' + split_time + "\n" + 'RegExp Execution time: ' + reg_time + "\n");

The Answer 12

4 people think this answer is useful

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

The Answer 13

4 people think this answer is useful

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) => {
  const commas = [...str].filter(letter => 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

The Answer 14

3 people think this answer is useful
s = 'dir/dir/dir/dir/'
for(i=l=0;i<s.length;i++)
if(s[i] == '/')
l++

The Answer 15

3 people think this answer is useful

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 < input.length; i++) {
    var index_of_sub = input.indexOf(input_letter, i);

    if (index_of_sub > -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 < input.length; i++) {

With:

for (var i = 0, input_length = input.length; i < input_length; i++) {

Interesting read discussing the above: http://www.erichynds.com/blog/javascript-length-property-is-a-stored-value

The Answer 16

3 people think this answer is useful

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

The Answer 17

2 people think this answer is useful

The fastest method seems to be via the index operator:

function charOccurances (str, char)
{
  for (var c = 0, i = 0, len = str.length; i < len; ++i)
  {
    if (str[i] == char)
    {
      ++c;
    }
  }
  return c;
}

console.log( charOccurances('example/path/script.js', '/') ); // 2

Or as a prototype function:

String.prototype.charOccurances = function (char)
{
  for (var c = 0, i = 0, len = this.length; i < len; ++i)
  {
    if (this[i] == char)
    {
      ++c;
    }
  }
  return c;
}

console.log( 'example/path/script.js'.charOccurances('/') ); // 2

The Answer 18

2 people think this answer is useful

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 < 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 < 10000; i++) {
        charCount1(s, c);
    }
    console.timeEnd('charCount1');
    
    console.time('charCount2');
    for(let i = 0; i < 10000; i++) {
        charCount2(s, c);
    }
    console.timeEnd('charCount2');
    
    console.time('charCount3');
    for(let i = 0; i < 10000; i++) {
        charCount2(s, c);
    }
    console.timeEnd('charCount3');
}

Results from a few runs:

 perfIt()
charCount1: 3.843ms
charCount2: 11.614ms
charCount3: 11.470ms
=> undefined
   perfIt()
charCount1: 3.006ms
charCount2: 8.193ms
charCount3: 7.941ms
=> undefined
   perfIt()
charCount1: 2.539ms
charCount2: 7.496ms
charCount3: 7.601ms
=> undefined
   perfIt()
charCount1: 2.654ms
charCount2: 7.540ms
charCount3: 7.424ms
=> undefined
   perfIt()
charCount1: 2.950ms
charCount2: 9.445ms
charCount3: 8.589ms

Update 2020-Oct-24: Still the case with Node.js 12 (play with it yourself here)

The Answer 19

1 people think this answer is useful

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.");
}

The Answer 20

1 people think this answer is useful

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;

The Answer 21

1 people think this answer is useful

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:

function count(s, c) {
  var n = 0;
  for (let x of s) {
    if (x == c)
      n++;
  }
  return n;
}

The Answer 22

1 people think this answer is useful

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!

The Answer 23

1 people think this answer is useful

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 < len; ++charIndex) {
  if (str[charIndex] === ',') {
    ++num;
  }
}

The Answer 24

0 people think this answer is useful

My solution:

function countOcurrences(str, value){
   var regExp = new RegExp(value, "gi");
   return str.match(regExp) ? str.match(regExp).length : 0;  
}

The Answer 25

0 people think this answer is useful

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;

The Answer 26

0 people think this answer is useful

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<str.length;i++){
      var count = 0;
      for(j=0;j<str.length;j++){
        if(str[i] === str[j]){
          count++;
        }
      }
      if(!obj.hasOwnProperty(str[i])){
        obj[str[i]] = count;
      }
    }
  }
  return obj;
}

The Answer 27

0 people think this answer is useful

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:

console.log(substring_count("Lorem ipsum dolar un sit amet.", "m "))

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;
}

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.

The Answer 28

0 people think this answer is useful
var a = "acvbasbb";
var b= {};
for (let i=0;i<a.length;i++){
    if((a.match(new RegExp(a[i], "g"))).length > 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.

The Answer 29

0 people think this answer is useful

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.

The Answer 30

0 people think this answer is useful

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 < 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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