php sentence boundaries detection

Question

I would like to divide a text into sentences in PHP. I'm currently using a regex, which brings ~95% accuracy and would like to improve by using a better approach. I've seen NLP tools that do that in Perl, Java, and C but didn't see anything that fits PHP. Do you know of such a tool?

Answer 1

An enhanced regex solution

Assuming you do care about handling: Mr. and Mrs. etc. abbreviations, then the following single regex solution works pretty well:

<?php // test.php Rev:20160820_1800
$split_sentences = '%(?#!php/i split_sentences Rev:20160820_1800)
    # Split sentences on whitespace between them.
    # See: http://stackoverflow.com/a/5844564/433790
    (?<=          # Sentence split location preceded by
      [.!?]       # either an end of sentence punct,
    | [.!?][\'"]  # or end of sentence punct and quote.
    )             # End positive lookbehind.
    (?<!          # But don\'t split after these:
      Mr\.        # Either "Mr."
    | Mrs\.       # Or "Mrs."
    | Ms\.        # Or "Ms."
    | Jr\.        # Or "Jr."
    | Dr\.        # Or "Dr."
    | Prof\.      # Or "Prof."
    | Sr\.        # Or "Sr."
    | T\.V\.A\.   # Or "T.V.A."
                 # Or... (you get the idea).
    )             # End negative lookbehind.
    \s+           # Split on whitespace between sentences,
    (?=\S)        # (but not at end of string).
    %xi';  // End $split_sentences.

$text = 'This is sentence one. Sentence two! Sentence thr'.
        'ee? Sentence "four". Sentence "five"! Sentence "'.
        'six"? Sentence "seven." Sentence \'eight!\' Dr. '.
        'Jones said: "Mrs. Smith you have a lovely daught'.
        'er!" The T.V.A. is a big project! '; // Note ws at end.

$sentences = preg_split($split_sentences, $text, -1, PREG_SPLIT_NO_EMPTY);
for ($i = 0; $i < count($sentences); ++$i) {
    printf("Sentence[%d] = [%s]\n", $i + 1, $sentences[$i]);
}
?>

Note that you can easily add or take away abbreviations from the expression. Given the following test paragraph:

This is sentence one. Sentence two! Sentence three? Sentence "four". Sentence "five"! Sentence "six"? Sentence "seven." Sentence 'eight!' Dr. Jones said: "Mrs. Smith you have a lovely daughter!" The T.V.A. is a big project!

Here is the output from the script:

Sentence[1] = [This is sentence one.]
Sentence[2] = [Sentence two!]
Sentence[3] = [Sentence three?]
Sentence[4] = [Sentence "four".]
Sentence[5] = [Sentence "five"!]
Sentence[6] = [Sentence "six"?]
Sentence[7] = [Sentence "seven."]
Sentence[8] = [Sentence 'eight!']
Sentence[9] = [Dr. Jones said: "Mrs. Smith you have a lovely daughter!"]
Sentence[10] = [The T.V.A. is a big project!]

The essential regex solution

The author of the question commented that the above solution "overlooks many options" and is not generic enough. I'm not sure what that means, but the essence of the above expression is about as clean and simple as you can get. Here it is:

$re = '/(?<=[.!?]|[.!?][\'"])\s+(?=\S)/';
$sentences = preg_split($re, $text, -1, PREG_SPLIT_NO_EMPTY);

Note that both solutions correctly identify sentences ending with a quotation mark after the ending punctuation. If you don't care about matching sentences ending in a quotation mark the regex can be simplified to just: /(?<=[.!?])\s+(?=\S)/.

Edit: 20130820_1000 Added T.V.A. (another punctuated word to be ignored) to regex and test string. (to answer PapyRef's comment question)

Edit: 20130820_1800 Tidied and renamed regex and added shebang. Also fixed regexes to prevent splitting text on trailing whitespace.