How Can I Split a String in C# While Keeping the Delimiters?

Preserving Delimiters When Splitting Strings in C#

Often, you need to split a string using specific delimiters, but you also want to keep those delimiters in the resulting array. This article demonstrates a reliable method in C# using regular expressions.

The Solution: Regular Expressions

C#'s Regex.Split method, combined with a cleverly crafted regular expression, provides the solution. The key is using positive lookbehind assertions. A positive lookbehind ensures a pattern exists before the current position without including that pattern in the match itself.

Regular Expression Pattern:

This pattern finds delimiters (commas, periods, and semicolons in this example) while ensuring they remain in the output:

(?<=(?:[,.;]))

• (?: This is a positive lookbehind assertion.
• (?:[,.;]): This is a non-capturing group matching a comma, period, or semicolon.

Code Example:

Let's illustrate with code:

using System.Text.RegularExpressions;

// ... other code ...

string originalString = "This,is,a,comma,separated,string.";

string[] parts = Regex.Split(originalString, @"(?<=(?:[,.;]))");

// parts array will contain:
// ["This",",","is",",","a",",","comma",",","separated",",","string","."] 

The regular expression splits the string at the points immediately following each delimiter. Because the delimiter itself isn't included in the match, it's preserved in the resulting array.

Output:

The output demonstrates that the original string is split, and each delimiter is included as a separate element in the resulting array. The positive lookbehind ensures delimiters are part of the split without being absorbed into the string segments.

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