The quickest regular expression match possible if it is already a subsection of another match

Question

The quickest regular expression match possible if it is already a subsection of another match

Is there a simple way to find the shortest match in a long text where strings are repeated? I'm having trouble because matches within already matched text aren't being found.

Here's an example of the issue:

Using code: "ababc".match(/a.+c/g)
Resulting in: ["ababc"]
Expected outcome: ["ababc", "abc"]

I am looking for a solution that doesn't involve manually writing recursive code to search within matches. Any ideas?

javascript regex

Answer 1

Answer №1

Like I mentioned earlier, using just regex won't achieve what you're trying to do.

You presented a basic example, so it's hard to say how useful this will be for your specific case. However, here is my attempt at addressing your needs. It seems like the characters "a" and "c" may vary, so you might have to adjust the code accordingly (e.g. pass them as arguments).

function findShortestMatch(str) {
  var str = str || '';
  var match,
    index,
    regex,
    length,
    results = [];
  
  for (index = 0, length = str.length; index < length; index++) {
    if (str[index] === 'a') {
      regex = new RegExp('^.{' + index + '}(a.+?c)');
      match = str.match(regex);
      
      if (match && match[1]) {
        results.push(match[1]);
      }
    }
  }

  results.sort(function(a, b){
    return a.length - b.length;
  });

  console.log(results);

  return results[0];
}

Example

findShortestMatch('ababcabbc');

// output of all matches found 
["abc", "abbc", "ababc"]

// result
"abc"

Note: This function prioritizes finding the shortest match between an 'a' and a 'c', rather than all possible matches. If you need all matches, including longer ones, consider using a greedy regex with .+.

Answer 2

Like I mentioned earlier, using just regex won't achieve what you're trying to do.

You presented a basic example, so it's hard to say how useful this will be for your specific case. However, here is my attempt at addressing your needs. It seems like the characters "a" and "c" may vary, so you might have to adjust the code accordingly (e.g. pass them as arguments).

function findShortestMatch(str) {
  var str = str || '';
  var match,
    index,
    regex,
    length,
    results = [];
  
  for (index = 0, length = str.length; index < length; index++) {
    if (str[index] === 'a') {
      regex = new RegExp('^.{' + index + '}(a.+?c)');
      match = str.match(regex);
      
      if (match && match[1]) {
        results.push(match[1]);
      }
    }
  }

  results.sort(function(a, b){
    return a.length - b.length;
  });

  console.log(results);

  return results[0];
}

Example

findShortestMatch('ababcabbc');

// output of all matches found 
["abc", "abbc", "ababc"]

// result
"abc"

Note: This function prioritizes finding the shortest match between an 'a' and a 'c', rather than all possible matches. If you need all matches, including longer ones, consider using a greedy regex with .+.

Answer 3

Answer №2

Iterate through each substring by starting from every character onwards (using the slice method), check for a match against a regular expression anchored to the beginning of the string (^), and employ non-greedy matching (?):

const input = "ababc";
const regexp = /^a.+?c/;

const results = [];
    
for (let i = 0; i < input.length; i++) {
  let match = input.slice(i).match(regexp);
  if (match) results.push(match[0]);
}

console.log("all found results:", results);
let shortestResult = results.sort((a, b) => a.length - b.length)[0];
console.log("the shortest result is:", shortestResult);

Answer 4

Iterate through each substring by starting from every character onwards (using the slice method), check for a match against a regular expression anchored to the beginning of the string (^), and employ non-greedy matching (?):

const input = "ababc";
const regexp = /^a.+?c/;

const results = [];
    
for (let i = 0; i < input.length; i++) {
  let match = input.slice(i).match(regexp);
  if (match) results.push(match[0]);
}

console.log("all found results:", results);
let shortestResult = results.sort((a, b) => a.length - b.length)[0];
console.log("the shortest result is:", shortestResult);

Answer 5

Answer №3

After careful consideration, I ultimately chose this particular solution for its impressive effectiveness, straightforwardness, and optimized performance:

let seq = "us warship";
let source = "The traditional US adversary has also positioned a spy ship off the coast of Delaware and carried out flights near a US Navy warship, concerning American officials.";

let re = new RegExp(`\\b${seq.replace(/\s/g, "\\b.+?\\b")}\\b`, "gi");
let snippet = null;
let matches;
while (matches = re.exec(source)) {
  let match = matches[0];
  if (!snippet || match.length < snippet.length) {
    snippet = match;
  }
  re.lastIndex -= (match.length - 1);
}
console.log(snippet); // "US Navy warship"

Source:

Answer 6

After careful consideration, I ultimately chose this particular solution for its impressive effectiveness, straightforwardness, and optimized performance:

let seq = "us warship";
let source = "The traditional US adversary has also positioned a spy ship off the coast of Delaware and carried out flights near a US Navy warship, concerning American officials.";

let re = new RegExp(`\\b${seq.replace(/\s/g, "\\b.+?\\b")}\\b`, "gi");
let snippet = null;
let matches;
while (matches = re.exec(source)) {
  let match = matches[0];
  if (!snippet || match.length < snippet.length) {
    snippet = match;
  }
  re.lastIndex -= (match.length - 1);
}
console.log(snippet); // "US Navy warship"

Source:

The quickest regular expression match possible if it is already a subsection of another match

Answer №1

Answer №2

Answer №3

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