JavaScript Program to Print the Frequency of Each Character in Alphabetical Order

In this article, we are going to implement a JavaScript program to print the frequency of each character in alphabetical order. This operation involves counting how many times each character (typically, alphabetic characters) appears in a given text and then displaying the results in alphabetical order.

Example:

Input: str = “aabccccddd” 
Output: a2b1c4d3 
Since it is already in alphabetical order, the frequency 
of the characters is returned for each character. 
Input: str = “geeksforgeeks” 
Output: e4f1g2k2o1r1s2 

Using Regular Expression

In this approach, we are using regular expressions to remove any non-alphabetic element from the string, then storing the alphabet and their respective frequencies in an object called frequency.

Syntax:

const cleanedString = inputString.replace(/[^a-z]/gi, '').toLowerCase();

Javascript

const printAlphabeticalFrequency = (
  inputString ) => {

  // Remove non-alphabetic characters
  // and convert to lowercase
  const cleanedString = inputString
    .replace(/[^a-z]/gi, "")
    .toLowerCase();

  // Create an object to store the
  // character frequencies
  const frequency = {};

  // Iterate through the cleaned string
  for (let char of cleanedString) {

    // If the character is not in the
    // frequency object, add it with a
    // count of 1
    if (!frequency[char]) {
      frequency[char] = 1;}
    else {

      // If the character is already
      // in the frequency object,
      // increment its count
      frequency[char]++;
  }}

  // Get an array of the characters
  // and sort them in alphabetical order
  const characters =
    Object.keys(frequency).sort();

  // Iterate through the sorted characters
  // and print their frequencies
  for (let char of characters) {
    console.log(
      char + ": " +
      frequency[char]
    );}
};

const inputString = "Geeks for Geeks";
printAlphabeticalFrequency(inputString);

Output

e: 4
f: 1
g: 2
k: 2
o: 1
r: 1
s: 2

Using a match() Method

In this approach, we are using the match method of JavaScript. It is an inbuilt method of JavaScript to search a string for a match against any regular expression. If the match is found, then this will return the match as an array.

Syntax:

const matches = cleanedString.match(new RegExp(char, 'g'));

Javascript

const printAlphabeticalFrequency = (
  inputString ) => {

  // Remove non-alphabetic characters
  // and convert to lowercase
  const cleanedString = inputString
    .replace(/[^a-z]/gi, "")
    .toLowerCase();

  // Create a string of all lowercase alphabets
  const alphabet =
    "abcdefghijklmnopqrstuvwxyz";

  // Initialize an object to store
  // character frequencies
  const frequency = {};

  // Iterate through the alphabet
  for (let char of alphabet) {

    // Use the match() function with a
    // regular expression to find all occurrences
    // of the character
    const matches =
      cleanedString.match(
        new RegExp(char, "g"));

    if (matches) {

      // If matches are found, store the
      // count in the frequency object
      frequency[char] =
        matches.length;
  }}

  // Iterate through the characters in
  // alphabetical order and print their frequencies
  for (let char of alphabet) {
    if (
      frequency[char] !==
      undefined) {
      console.log(
        char + ": " +
        frequency[char]
      );
}}};

const inputString = "GeeksForGeeks";
printAlphabeticalFrequency(inputString);

Output

e: 4
f: 1
g: 2
k: 2
o: 1
r: 1
s: 2