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

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Implementations

C++

 #include <algorithm>
 #include <string>
 using namespace std;
 int main() {
     string str("Count, the number,, of commas.");
     int count = count(str.begin(), str.end(), ',');
 }

D

import std.string: count;
void main() {
    string s = "Count, the number,, of commas.";
    auto numberOfCommas = s.count(",");
}

Erlang

-module(codex).
-export([count_chr/2]).
count_chr(String, Chr) ->
    F = fun(X, N) when X =:= Chr -> N + 1;
           (_, N)                -> N
        end,
    lists:foldl(F, 0, String).

The use example 

codex:count_chr("Count, the number,, of commas.", $,).

Go

    s := "Count, the number,, of commas."
    n := 0
    for _, c := range s { 
        if c == ',' {
            n++ 
        }   
    }   
    fmt.Println(n)

Haskell

countOfElem elem list = length $ filter (\x -> x == elem) list

or more point-free 

countOfElem elem = length . filter (==elem)

In ghci: 

*Main> countOfElem 'i' "Veni vidi vici"
5

JavaScript

Implementation 1

This is the function: 

String.prototype.count=function(s1) { 
	return (this.length - this.replace(new RegExp(s1,"g"), '').length) / s1.length;
}

Use it like this: 

// use like this 
test = "this, as you see, is a sentence, containing many ','s";
numberOfCommas = test.count(','); //4
// or 
numberOfSblank = test.count('s '); //2

Implementation 2

First, create a new function called replaceAll: 

String.prototype.replaceAll=function(s1, s2) { 
	return this.replace(new RegExp(s1,"g"), s2);
}

Then you can use this function to count the occurrence of a specific character or string within another string. For example, this code counts the number of commas within a string. To count a different character, replace the comma in '[^,]' to another character, such as a lowercase x ('[^x]'). 

        numberOfCommas = text.replaceAll('[^,]','').length + 1;

Implementation 3

Another way to do it without RegExp: 

String.prototype.count = function(char){
    return this.split(char).length-1;
}

Implementation 4

Without functions and without RegExp 

 ('ab,cd,ef'.split(',').length - 1)

Java

There are multiple solutions. For such a low level task you should probably do a performance test to see which method is faster. For instance, regular expressions are very slow in java.

Implementation 1

This code will count the number of commas in a string. 

	String s = "Count, the number,, of commas.";
	int numberOfCommas = s.replaceAll("[^,]","").length();

Implementation 2

public int count(String input, String countString){
  return input.split("\\Q"+countString+"\\E", -1).length - 1;
}

Implementation 3

public int count(String sourceString, char lookFor) {
    if (sourceString == null) {
        return -1;
    }
    int count = 0;
    for (int i = 0; i < sourceString.length(); i++) {
        final char c = sourceString.charAt(i);
        if (c == lookFor) {
            count++;
        }
    }
    return count;
}

Implementation 4

public static int count(String word, Character ch)
{
	int pos = word.indexOf(ch);
	return pos == -1 ? 0 : 1 + count(word.substring(pos+1),ch);
}

Perl

$count = () = $string =~ /colou?r/g; # count the number of  colours (and colors).

$count = $string =~ tr/,//; # count the number of commas. this does not modify the string in any way

Python

This code will count the number of commas in a string. 

s = "Count, the number,, of commas."
print s.count(",")

PHP

PHP has a built-in function for this called substr_count. 

<?php
$text = 'This is a test';
echo strlen($text); // 14

echo substr_count($text, 'is'); // 2

// the string is reduced to 's is a test', so it prints 1
echo substr_count($text, 'is', 3);

// the text is reduced to 's i', so it prints 0
echo substr_count($text, 'is', 3, 3);

// generates a warning because 5+10 > 14
echo substr_count($text, 'is', 5, 10);


// prints only 1, because it doesn't count overlapped subtrings
$text2 = 'gcdgcdgcd';
echo substr_count($text2, 'gcdgcd');
?>

Ruby

s = "Count, the number,, of commas."
puts s.count(",")

Tcl 

set s "Count, the number,, of commas."
puts [expr {[llength [split $s ","]] - 1}]

Zsh

count() {
	local string char
	string="Count, the number,, of commas."
	char=${string//[^,]/}
	print ${(c)#char}	
}

Other titles

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  • string char count
  • number of occurrences in a string
  • character count for strings
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