Counting Each Letter's Frequency in a String

Counting each letter's frequency in a string

In 2.7+:

import collections
letters = collections.Counter('google')

Earlier (2.5+, that's ancient by now):

import collections
letters = collections.defaultdict(int)
for letter in word:
    letters[letter] += 1

how to count the frequency of letters in text excluding whitespace and numbers?

This should work:

>>> from collections import Counter
>>> from string import ascii_letters
>>> def count_letters(s) :
...     filtered = [c for c in s.lower() if c in ascii_letters]
...     return Counter(filtered)
... 
>>> count_letters('Math is fun! 2+2=4')
Counter({'a': 1, 'f': 1, 'i': 1, 'h': 1, 'm': 1, 'n': 1, 's': 1, 'u': 1, 't': 1})
>>> 

Python - Counting Letter Frequency in a String

Does this satisfy your needs?

from itertools import groupby
s = "bbbaaac ddddee aa"

groups = groupby(s)
result = [(label, sum(1 for _ in group)) for label, group in groups]
res1 = "".join("{}{}".format(label, count) for label, count in result)
# 'b3a3c1 1d4e2 1a2'

# spaces just as spaces, do not include their count
import re
re.sub(' [0-9]+', ' ', res1)
'b3a3c1 d4e2 a2'

Counting frequency of characters in a string using JavaScript

Here you go:

function getFrequency(string) {
    var freq = {};
    for (var i=0; i<string.length;i++) {
        var character = string.charAt(i);
        if (freq[character]) {
           freq[character]++;
        } else {
           freq[character] = 1;
        }
    }

    return freq;
};

What's the most efficient way to calculate frequency of each letter in a string C++?

You can omit std::set and just write like so

int main() {
    std::string s;
    std::cin >> s;
    int cnt[26] = {};

    for (int i = 0; i < s.length(); i++) {
        cnt[s[i] - 'a']++;
    }
    for (int i = 0; i < 26; ++i) 
        if (cnt[i] > 0)
            std::cout << (char)('a' + i) << " : " << cnt[i] << std::endl;

    return 0;
}

Instead saving in the std::set, we check the presence of a character in the cnt and to output if a symbol was.

This option takes less memory.

Counting Character Frequency in String(Java)

Well, count is an int[] with 256 slots:

int count[] = new int[MAX_CHAR]; // MAX_CHAR is 256

Your algorithm defines MAX_CHAR = 256, because it assumes the string consists only of 8-Bit ASCII characters.

[0, 0, ..., 0, 0] // 256 slots

Now you're iterating each character in string str and cast it to an integer (see type casting of primitives in Java). An A will be casted to 65 (ASCII table), a B to 66 and so on. The casted int is the slot to increment. So a string A would lead to an increment of the integer at index 65. Your question was primarily about

count[str.charAt(i)]++

That translates to this:

char c = str.charAt(i);    // c = A
int index = c;             // c = A, casted to an int = 65
count[index]++             // increments the int at position 65

Result:

[0, 0, ..., 1, ..., 0, 0]
            ^ index 65

The next A would increment the int at index 65 again:

[0, 0, ..., 2, ..., 0, 0]
            ^ index 65

count the frequency of each character using the dictionary in python

You can iterate over string and update the dictionary accordingly and also there's no need of any count variable.

test_str = input().lower()
dicx = {} 
  
for i in test_str: 
    if i in dicx: 
        dicx[i] += 1
    else: 
        dicx[i] = 1

print(dicx)

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