What is a regular expression for parsing out individual sentences?

Question

I am looking for a good .NET regular expression that I can use for parsing out individual sentences from a body of text.

It should be able to parse the following block of text into exactly six sentences:

Hello world! How are you? I am fine. This is a difficult sentence because I use I.D.  Newlines should also be accepted. Numbers should not cause   sentence breaks, like 1.23. 

This is proving a little more challenging than I originally thought.

Any help would be greatly appreciated. I am going to use this to train the system on known bodies of text.

Answer 1

Try this @"(\S.+?[.!?])(?=\s+|$)":

string str=@"Hello world! How are you? I am fine. This is a difficult sentence because I use I.D. Newlines should also be accepted. Numbers should not cause sentence breaks, like 1.23.";  Regex rx = new Regex(@"(\S.+?[.!?])(?=\s+|$)"); foreach (Match match in rx.Matches(str)) {     int i = match.Index;     Console.WriteLine(match.Value); } 

Results:

Hello world! How are you? I am fine. This is a difficult sentence because I use I.D. Newlines should also be accepted. Numbers should not cause sentence breaks, like 1.23. 

For complicated ones, of course, you will need a real parser like SharpNLP or NLTK. Mine is just a quick and dirty one.

Here is the SharpNLP info, and features:

SharpNLP is a collection of natural language processing tools written in C#. Currently it provides the following NLP tools:

• a sentence splitter
• a tokenizer
• a part-of-speech tagger
• a chunker (used to "find non-recursive syntactic annotations such as noun phrase chunks")
• a parser
• a name finder
• a coreference tool
• an interface to the WordNet lexical database

Answer 2

var str = @"Hello world! How are you? I am fine. This is a difficult sentence because I use I.D. Newlines should also be accepted. Numbers should not cause sentence breaks, like 1.23.";  Regex.Split(str, @"(?<=[.?!])\s+").Dump(); 

I tested this in LINQPad.