How to Count the Number of Occurrences of a Char in a String

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

Simple way to count character occurrences in a string

public int countChar(String str, char c)
{
    int count = 0;

    for(int i=0; i < str.length(); i++)
    {    if(str.charAt(i) == c)
            count++;
    }

    return count;
}

This is definitely the fastest way. Regexes are much much slower here, and possible harder to understand.

Count number of occurrences for each char in a string

This is really, really simple in JavaScript (or any other language that supports maps):

// The string
var str = "I want to count the number of occurrences of each char in this string";

// A map (in JavaScript, an object) for the character=>count mappings
var counts = {};

// Misc vars
var ch, index, len, count;

// Loop through the string...
for (index = 0, len = str.length; index < len; ++index) {
    // Get this character
    ch = str.charAt(index); // Not all engines support [] on strings

    // Get the count for it, if we have one; we'll get `undefined` if we
    // don't know this character yet
    count = counts[ch];

    // If we have one, store that count plus one; if not, store one
    // We can rely on `count` being falsey if we haven't seen it before,
    // because we never store falsey numbers in the `counts` object.
    counts[ch] = count ? count + 1 : 1;
}

Now counts has properties for each character; the value of each property is the count. You can output those like this:

for (ch in counts) {
    console.log(ch + " count: " + counts[ch]);
}

Is there a better way to count occurrence of char in a string?

Counting the occurences of a character in a string can be performed with one line in Perl (as compared to your 4 lines). There is no need for a sub (although there is nothing wrong with encapsulating functionality in a sub). From perlfaq4 "How can I count the number of occurrences of a substring within a string?"

use warnings;
use strict;

my $str = "ru8xysyyyyyyysss6s5s";
my $char = "y";
my $count = () = $str =~ /\Q$char/g;
print "count<$count> of <$char> in <$str>\n";

How to count number of occurrences of a certain char in string?

You can use this simple function:

function OccurrencesOfChar(const S: string; const C: char): integer;
var
  i: Integer;
begin
  result := 0;
  for i := 1 to Length(S) do
    if S[i] = C then
      inc(result);
end;

Count the occurrence of characters in a string

so i figured out how to do it without using sets and counters.

S = (input("Enter a string: "))
S = S.lower()
alpha = "abcdefghijklmnopqrstuvwxyz!@#$%^&*()! "
L = []
#counts the occurrence of characters in a string.
#then puts them in a list
for char in S:
     if char in alpha:
          count = S.count(char)
     L.append(char)
     L.append(count)
#turns list into a nested list
L2 = []
i = 0
while i <len(L):
        L2.append(L[i:i+2])
        i += 2
#checks that the lists dont appear more than once 
L3 = []
for i in L2:
     if i not in L3:
          L3.append(i)

# print out the letters and count of the letter
for i,k in L3:
     print(i,k)

might be long but it works. would like your opinion on it?

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