How to resolve the algorithm Split a character string based on change of character step by step in the JavaScript programming language

Published on 12 May 2024 09:40 PM
#Javascript

How to resolve the algorithm Split a character string based on change of character step by step in the JavaScript programming language

Table of Contents

Problem Statement

Split a (character) string into comma (plus a blank) delimited strings based on a change of character   (left to right). Show the output here   (use the 1st example below).

Blanks should be treated as any other character   (except they are problematic to display clearly).   The same applies to commas.

For instance, the string: should be split and show:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Split a character string based on change of character step by step in the JavaScript programming language

Explanation:

This JavaScript code snippet demonstrates two different ways to split a string into groups of characters based on changes in the characters.

Split on Character Changes (First Function):

The main function takes a string as input and uses the group function to split it into groups of characters. The group function takes a list of characters and returns a list of lists, where each sublist contains only elements that are equal to each other (===).

The code then calls join on each sublist to concatenate the characters back into strings and joins the resulting strings with commas.

Split on Character Changes (Second Function):

This function also takes a string as input and uses the charGroups function to split it into groups of characters. The charGroups function is recursive and operates as follows:

  • It checks if the string is empty. If it is, it returns an empty string.
  • If not, it takes the first character of the string and splits the remaining string into two parts: one containing characters that are the same as the first character, and the other containing characters that are different.
  • It recursively calls charGroups on the second part and returns a list of strings consisting of the first character, followed by the characters in the first part, followed by the groups of characters returned by the recursive call.
  • It joins the characters in each sublist back into strings and returns the resulting list.

The main function then calls charGroups on the input string and joins the resulting groups with commas.

Generic Functions:

Both functions use some generic functions:

  • groupBy: Splits a list of elements into groups based on an equality operation.
  • span: Splits a list into two parts: one containing elements that satisfy a predicate, and the other containing the remaining elements.
  • Tuple: Creates a tuple (a pair) of elements.

Overall, this code provides two ways to split a string into groups of characters based on changes in the characters.

Source code in the javascript programming language

(() => {
    "use strict";

    // ----------- SPLIT ON CHARACTER CHANGES ------------
    const main = () =>
        group("gHHH5YY++///\\")
        .map(x => x.join(""))
        .join(", ");


    // --------------------- GENERIC ---------------------

    // group :: [a] -> [[a]]
    const group = xs =>
        // A list of lists, each containing only
        // elements equal under (===), such that the
        // concatenation of these lists is xs.
        groupBy(a => b => a === b)(xs);


    // groupBy :: (a -> a -> Bool) [a] -> [[a]]
    const groupBy = eqOp =>
        // A list of lists, each containing only elements
        // equal under the given equality operator,
        // such that the concatenation of these lists is xs.
        xs => 0 < xs.length ? (() => {
            const [h, ...t] = xs;
            const [groups, g] = t.reduce(
                ([gs, a], x) => eqOp(x)(a[0]) ? (
                    Tuple(gs)([...a, x])
                ) : Tuple([...gs, a])([x]),
                Tuple([])([h])
            );

            return [...groups, g];
        })() : [];


    // Tuple (,) :: a -> b -> (a, b)
    const Tuple = a =>
        b => ({
            type: "Tuple",
            "0": a,
            "1": b,
            length: 2,
            *[Symbol.iterator]() {
                for (const k in this) {
                    if (!isNaN(k)) {
                        yield this[k];
                    }
                }
            }
        });

    // MAIN ---
    return main();
})();


(() => {
    "use strict";

    // -------- STRING SPLIT ON CHARACTER CHANGES --------

    // charGroups :: String -> [String]
    const charGroups = s =>
        // The characters of s split at each point where
        // consecutive characters differ.
        0 < s.length ? (() => {
            const
                c = s[0],
                [xs, ys] = span(x => c === x)([
                    ...s.slice(1)
                ]);

            return [
                    [c, ...xs], ...charGroups(ys)
                ]
                .map(zs => [...zs].join(""));
        })() : "";


    // ---------------------- TEST -----------------------
    // main :: IO()
    const main = () =>
        charGroups("gHHH5YY++///\\")
        .join(", ");


    // --------------------- GENERIC ---------------------

    // span :: (a -> Bool) -> [a] -> ([a], [a])
    const span = p =>
        // Longest prefix of xs consisting of elements which
        // all satisfy p, tupled with the remainder of xs.
        xs => {
            const i = xs.findIndex(x => !p(x));

            return -1 !== i ? [
                xs.slice(0, i),
                xs.slice(i)
            ] : [xs, []];
        };

    // MAIN ---
    return main();
})();

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