C# split string but keep separators

Question

There already exist similar questions, but all of them use regexen. The code I'm using (that strips the separators):

string[] sentences = s.Split(new string[] { ". ", "? ", "! ", "... " }, StringSplitOptions.None);

I would like to split a block of text on sentence breaks and keep the sentence terminators. I'd like to avoid using regexen for performance. Is it possible?

Funny. The title of the duplicate is "C# split string but keep split chars". — user166390
– user166390, Commented Apr 11, 2011 at 17:56
@rerun: This will be ran on a very large file and regex splitting takes up to three times as long as the String methods. — Isaac G.
– Isaac G., Commented Apr 11, 2011 at 18:00

JaredPar · Accepted Answer · 2011-04-11 17:59:59Z

6

I don't believe there is an existing function that does this. However you can use the following extension method.

public static IEnumerable<string> SplitAndKeepSeparators(this string source, string[] separators) {
  var builder = new Text.StringBuilder();
  foreach (var cur in source) {
    builder.Append(cur);
    if (separators.Contains(cur)) {
      yield return builder.ToString();
      builder.Length = 0;
    }
  }
  if (builder.Length > 0) {
    yield return builder.ToString();
  }
}

edited Apr 11, 2011 at 17:59

answered Apr 11, 2011 at 17:52

JaredPar

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5 Comments

user166390 Over a year ago

It seems like this will break for the last field?

JaredPar Over a year ago

@jfs, @pst whoops, forgot to add in the final check

Isaac G. Over a year ago

if (separators.Contains(cur)) won't compile.

user166390 Over a year ago

@Isaac G. using System.Linq; (This is because Contains is an Extension Method from LINQ)

Timwi Over a year ago

This is completely broken. “cur” is a char, “separators” is a string[]. “separators.Contains(cur)” makes no sense.

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