Frequency distribution of elements - JavaScript

We are required to write a JavaScript function that takes a string and returns an object representing the frequency distribution of each character in the string.

const str = 'This string will be used to calculate frequency distribution';

We need to return an object that represents the frequency distribution of various characters present in the string.

Example

Following is the code:

const str = 'This string will be used to calculate frequency distribution';

const frequencyDistribution = str => {
    const map = {};
    for(let i = 0; i < str.length; i++){
        map[str[i]] = (map[str[i]] || 0) + 1;
    };
    return map;
};

console.log(frequencyDistribution(str));

Output

Following is the output in the console:

{
    T: 1,
    h: 1,
    i: 6,
    s: 4,
    ' ': 8,
    t: 5,
    r: 3,
    n: 3,
    g: 1,
    w: 1,
    l: 4,
    b: 2,
    e: 5,
    u: 4,
    d: 2,
    o: 2,
    c: 3,
    a: 2,
    f: 1,
    q: 1,
    y: 1
}

How It Works

The function iterates through each character in the string using a for loop. For each character, it either initializes the count to 1 (if the character hasn't been seen before) or increments the existing count by 1. The expression (map[str[i]] || 0) + 1 handles both cases efficiently.

Alternative Approach Using for...of Loop

const str = 'hello world';

const frequencyDistribution = str => {
    const map = {};
    for(const char of str){
        map[char] = (map[char] || 0) + 1;
    }
    return map;
};

console.log(frequencyDistribution(str));

{
    h: 1,
    e: 1,
    l: 3,
    o: 2,
    ' ': 1,
    w: 1,
    r: 1,
    d: 1
}

Using Array.reduce() Method

const str = 'javascript';

const frequencyDistribution = str => {
    return str.split('').reduce((acc, char) => {
        acc[char] = (acc[char] || 0) + 1;
        return acc;
    }, {});
};

console.log(frequencyDistribution(str));

{
    j: 1,
    a: 2,
    v: 1,
    s: 1,
    c: 1,
    r: 1,
    i: 1,
    p: 1,
    t: 1
}

Conclusion

Character frequency distribution can be efficiently calculated using object mapping. The for loop approach is straightforward, while the reduce method provides a more functional programming style.