Split string into sentences in javascript

Currently i am working on an application that splits a long column into short ones. For that i split the entire text into words, but at the moment my regex splits numbers too.

What i do is this:

str = "This is a long string with some numbers [125.000,55 and 140.000] and an end. This is another sentence.";
sentences = str.replace(/\.+/g,'.|').replace(/\?/g,'?|').replace(/\!/g,'!|').split("|");

The result is:

Array [
    "This is a long string with some numbers [125.",
    "000,55 and 140.",
    "000] and an end.",
    " This is another sentence."
]

The desired result would be:

Array [
    "This is a long string with some numbers [125.000, 140.000] and an end.",
    "This is another sentence"
]

How do i have to change my regex to achieve this? Do i need to watch out for some problems i could run into? Or would it be good enough to search for ". ", "? " and "! "?

str.replace(/([.?!])\s*(?=[A-Z])/g, "$1|").split("|")

Output:

[ 'This is a long string with some numbers [125.000,55 and 140.000] and an end.',
  'This is another sentence.' ]

Breakdown:

([.?!]) = Capture either . or ? or !

\s* = Capture 0 or more whitespace characters following the previous token ([.?!]). This accounts for spaces following a punctuation mark which matches the English language grammar.

(?=[A-Z]) = The previous tokens only match if the next character is within the range A-Z (capital A to capital Z). Most English language sentences start with a capital letter. None of the previous regexes take this into account.

The replace operation uses:

"$1|"

We used one "capturing group" ([.?!]) and we capture one of those characters, and replace it with $1 (the match) plus |. So if we captured ? then the replacement would be ?|.

Finally, we split the pipes | and get our result.

So, essentially, what we are saying is this:

1) Find punctuation marks (one of . or ? or !) and capture them

2) Punctuation marks can optionally include spaces after them.

3) After a punctuation mark, I expect a capital letter.

Unlike the previous regular expressions provided, this would properly match the English language grammar.

From there:

4) We replace the captured punctuation marks by appending a pipe |

5) We split the pipes to create an array of sentences.

str.replace(/(\.+|\:|\!|\?)(\"*|\'*|\)*|}*|]*)(\s|\n|\r|\r\n)/gm, "$1$2|").split("|")

The RegExp (see on Debuggex):

• (.+|:|!|\?) = The sentence can end not only by ".", "!" or "?", but also by "..." or ":"
• (\"|\'|)*|}|]) = The sentence can be surrounded by quatation marks or parenthesis
• (\s|\n|\r|\r\n) = After a sentense have to be a space or end of line
• g = global
• m = multiline

Remarks:

• If you use (?=[A-Z]), the the RegExp will not work correctly in some languages. E.g. "Ü", "Č" or "Á" will not be recognised.

You could exploit that the next sentence begins with an uppercase letter or a number.

.*?(?:\.|!|\?)(?:(?= [A-Z0-9])|$)

Debuggex Demo

It splits this text

This is a long string with some numbers [125.000,55 and 140.000] and an end. This is another sentence. Sencenes beginning with numbers work. 10 people like that.

into the sentences:

This is a long string with some numbers [125.000,55 and 140.000] and an end.
This is another sentence.
Sencenes beginning with numbers work.
10 people like that.

jsfiddle

Use lookahead to avoid replacing dot if not followed by space + word char:

sentences = str.replace(/(?=\s*\w)\./g,'.|').replace(/\?/g,'?|').replace(/\!/g,'!|').split("|");

OUTPUT:

["This is a long string with some numbers [125.000,55 and 140.000] and an end. This is another sentence."]

You're safer using lookahead to make sure what follows after the dot is not a digit.

var str ="This is a long string with some numbers [125.000,55 and 140.000] and an end. This is another sentence."

var sentences = str.replace(/\.(?!\d)/g,'.|');
console.log(sentences);

If you want to be even safer you could check if what is behind is a digit as well, but since JS doesn't support lookbehind, you need to capture the previous character and use it in the replace string.

var str ="This is another sentence.1 is a good number"

var sentences = str.replace(/\.(?!\d)|([^\d])\.(?=\d)/g,'$1.|');
console.log(sentences);

An even simpler solution is to escape the dots inside numbers (replace them with $$$$ for example), do the split and afterwards unescape the dots.