CODEWITHSUNDEEP
javascriptregex
Gordo
Gordo

Reputation: 789

Get current sentence by cursor/caret position

I have a string containing multiple sentences. I also have the current cursor/caret position.

I need to be able to extract the current sentence at the given cursor position.

For example, take this string:

This is the first sentence. And this is the second! Finally, this is the third sentence

If the current cursor position is 33 then the cursor is in the second sentence.

In which case, the result returned should be:

And this is the second!

I only need to use the standard sentence definers of .?!

Any help with this would be greatly appreciated.

Although I am expecting regex to be required, if there is a faster alternative using native methods I would be interested in that also.

Upvotes: 2

Views: 220

Answers (3)

Useless Code
Useless Code

Reputation: 12422

I wanted to add an answer that doesn't use regular expression to split up the string because doing so is quite inefficient and would likely be very slow on larger chunks of text.

The most efficient way to do it would probably be to use a couple of loops to search, requiring only 2 passes to find the ends of the sentence.

var sentenceFromPos = function (s, pos) {
  var len = s.length,
    start,
    end,
    char;

  start = pos;
  end = pos;

  while (start >= 0) {
    char = s.charAt(start);
    if (char === '.' || char === '?' || char === '!') {
      break;
    }
    start -= 1;
  }

  while (end < len) {
    char = s.charAt(end);
    if (char === '.' || char === '?' || char === '!') {
      break;
    }
    end += 1;
  }

  return s.substring(start + 1, end + 1).trim();
};

var phrase = 'This is the first sentence.  And this is the second! Finally, this is the third sentence';

console.log(sentenceFromPos(phrase, 10));
console.log(sentenceFromPos(phrase, 33));
console.log(sentenceFromPos(phrase, 53));

Upvotes: 1

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627419

Here is a way to achieve what you need: use String#split with /[?!.]/g to get an array of sentences and then iterate over the array to sum up the lengths of the sentences found, and if the index is smaller than the count, return the sentence.

function getSentenceByPos(idx, str) {
    pos = 0;
    array = str.split(/[?!.]/g);
    for (var i=0; i<array.length; i++) {
 		pos += array[i].length + 1;
        if (pos >= idx) {
            return array[i];
        }
	}
}// 26 still 1 then `.`. 51 then `!` - 53 is 3rd sentence!
document.write(getSentenceByPos(53, "This is the first sentence.  And this is the second! Finally, this is the third sentence"));

Upvotes: 1

Amarnasan
Amarnasan

Reputation: 15579

This function will respect cursors over the limits of the phrases (like ! or .)

function getPhrase(string, cursor) {
    phrases = string.match(/.*?(!|\.|$)/g)
    basecursor = 0;
    phrase = phrases[0]
    for(ii=0; ii<phrases.length-1; ii++) {
        if (basecursor+phrases[ii].length<cursor) {
            phrase = phrases[ii+1]
            basecursor += phrases[ii].length
        }
    }
    return(phrase)
}
string = "This is the first sentence.  And this is the second! Finally, this is the third sentence"
cursor = 0
phrase = getPhrase(string, cursor)
document.write(phrase)

Upvotes: 0

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