How to resolve the algorithm Multisplit step by step in the JavaScript programming language

Published on 12 May 2024 09:40 PM
#Javascript

How to resolve the algorithm Multisplit step by step in the JavaScript programming language

Table of Contents

Problem Statement

It is often necessary to split a string into pieces based on several different (potentially multi-character) separator strings, while still retaining the information about which separators were present in the input. This is particularly useful when doing small parsing tasks. The task is to write code to demonstrate this. The function (or procedure or method, as appropriate) should take an input string and an ordered collection of separators. The order of the separators is significant: The delimiter order represents priority in matching, with the first defined delimiter having the highest priority. In cases where there would be an ambiguity as to which separator to use at a particular point (e.g., because one separator is a prefix of another) the separator with the highest priority should be used. Delimiters can be reused and the output from the function should be an ordered sequence of substrings. Test your code using the input string “a!===b=!=c” and the separators “==”, “!=” and “=”. For these inputs the string should be parsed as "a" (!=) "" (==) "b" (=) "" (!=) "c", where matched delimiters are shown in parentheses, and separated strings are quoted, so our resulting output is "a", empty string, "b", empty string, "c". Note that the quotation marks are shown for clarity and do not form part of the output. Extra Credit: provide information that indicates which separator was matched at each separation point and where in the input string that separator was matched.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Multisplit step by step in the JavaScript programming language

The provided JavaScript code is a set of functions used for advanced string splitting. It includes functions for splitting strings by various delimiters, escaping special characters, and applying generic array transformations. Here's a detailed breakdown:

  1. RegExp.escape: This function escapes special characters in a string to make it safe for use in regular expressions. It replaces characters like [, ], *, and . with their escaped versions.

  2. multisplit: This function splits a string into parts based on a list of delimiters. It uses a regular expression constructed from the escaped delimiters to perform the split.

  3. multiSplit: This is a more advanced string splitting function that takes a string and a list of delimiters as input and returns an array of objects. Each object represents a part of the split string, along with the delimiter that separated it. It uses various functional programming techniques for array manipulation and string processing.

  4. Generic Functions: The provided code also includes a set of generic array transformation functions, such as append, chars, drop, find, foldl, intercalate, isPrefixOf, just, length, map, nothing, and show. These functions are used in the multiSplit implementation for array manipulation, string processing, and data transformation.

The code also includes a test case where it splits a sample string using the defined delimiters and prints the results.

Source code in the javascript programming language

RegExp.escape = function(text) {
    return text.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&");
}

multisplit = function(string, seps) {
    var sep_regex = RegExp(_.map(seps, function(sep) { return RegExp.escape(sep); }).join('|'));
    return string.split(sep_regex);
}


(() => {

    /// Delimiter list -> String -> list of parts, delimiters, offsets

    // multiSplit :: [String] -> String ->
    //      [{part::String, delim::String, offset::Int}]
    const multiSplit = (ds, s) => {
        const
            dcs = map(chars, ds),
            xs = chars(s),
            dct = foldl(
                (a, c, i, s) => {
                    const
                        inDelim = a.offset > i,
                        mb = inDelim ? (
                            nothing('')
                        ) : find(d => isPrefixOf(d, drop(i, xs)), dcs);
                    return mb.nothing ? {
                        tokens: a.tokens.concat(inDelim ? (
                            []
                        ) : [c]),
                        parts: a.parts,
                        offset: a.offset
                    } : {
                        tokens: [],
                        parts: append(a.parts, [{
                            part: intercalate('', a.tokens),
                            delim: intercalate('', mb.just),
                            offset: i
                        }]),
                        offset: i + length(mb.just)
                    };
                }, {
                    tokens: [],
                    parts: [],
                    offset: 0
                }, xs
            );
        return append(dct.parts, [{
            part: intercalate('', dct.tokens),
            delim: "",
            offset: length(s)
        }]);
    };

    // GENERIC FUNCTIONS -----------------------------------------------------

    // append (++) :: [a] -> [a] -> [a]
    const append = (xs, ys) => xs.concat(ys);

    // chars :: String -> [Char]
    const chars = s => s.split('');

    // drop :: Int -> [a] -> [a]
    // drop :: Int -> String -> String
    const drop = (n, xs) => xs.slice(n);

    // find :: (a -> Bool) -> [a] -> Maybe a
    const find = (p, xs) => {
        for (var i = 0, lng = xs.length; i < lng; i++) {
            var x = xs[i];
            if (p(x)) return just(x);
        }
        return nothing('Not found');
    };

    // foldl :: (a -> b -> a) -> a -> [b] -> a
    const foldl = (f, a, xs) => xs.reduce(f, a);

    // intercalate :: String -> [String] -> String
    const intercalate = (s, xs) => xs.join(s);

    // isPrefixOf takes two lists or strings and returns
    // true iff the first is a prefix of the second.
    // isPrefixOf :: [a] -> [a] -> Bool
    // isPrefixOf :: String -> String -> Bool
    const isPrefixOf = (xs, ys) => {
        const pfx = (xs, ys) => xs.length ? (
            ys.length ? xs[0] === ys[0] && pfx(
                xs.slice(1), ys.slice(1)
            ) : false
        ) : true;
        return typeof xs !== 'string' ? pfx(xs, ys) : ys.startsWith(xs);
    };

    // just :: a -> Just a
    const just = x => ({
        nothing: false,
        just: x
    });

    // length :: [a] -> Int
    const length = xs => xs.length;

    // map :: (a -> b) -> [a] -> [b]
    const map = (f, xs) => xs.map(f);

    // nothing :: () -> Nothing
    const nothing = (optionalMsg) => ({
        nothing: true,
        msg: optionalMsg
    });

    // show :: Int -> a -> Indented String
    // show :: a -> String
    const show = (...x) =>
        JSON.stringify.apply(
            null, x.length > 1 ? [x[1], null, x[0]] : x
        );

    // TEST ------------------------------------------------------------------
    const
        strTest = 'a!===b=!=c',
        delims = ['==', '!=', '='];

    return show(2,
        multiSplit(delims, strTest)
    );
})();

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