Group Class

Definition

Represents the results from a single capturing group.

public class Group : System.Text.RegularExpressions.Capture
Inheritance
Derived
System.Text.RegularExpressions.Match

Inherited Members

System.Object

System.Text.RegularExpressions.Capture

Remarks

A capturing group can capture zero, one, or more strings in a single match because of quantifiers. (For more information, see Quantifiers.) All the substrings matched by a single capturing group are available from the Group.Captures property. Information about the last substring captured can be accessed directly from the Value and Index properties. (That is, the Group instance is equivalent to the last item of the collection returned by the Captures property, which reflects the last capture made by the capturing group.)

An example helps to clarify this relationship between a Group object and the CaptureCollection that is returned by the Captures property. The regular expression pattern (\b(\w+?)[,:;]?\s?)+[?.!] matches entire sentences. The regular expression is defined as shown in the following table.

Pattern Description
\b Begin the match at a word boundary.
(\w+?) Match one or more word characters, but as few characters as possible. This is the second (inner) capturing group. (The first capturing group includes the \b language element.)
[,:;]? Match zero or one occurrence of a comma, colon, or semicolon.
\s? Match zero or one occurrence of a white-space character.
(\b(\w+?)[,:;]?\s?)+ Match the pattern consisting of a word boundary, one or more word characters, a punctuation symbol, and a white-space character one or more times. This is the first capturing group.
[?.!] Match any occurrence of a period, question mark, or exclamation point.

In this regular expression pattern, the subpattern (\w+?) is designed to match multiple words within a sentence. However, the value of the Group object represents only the last match that (\w+?) captures, whereas the Captures property returns a CaptureCollection that represents all captured text. As the output shows, the CaptureCollection for the second capturing group contains four objects. The last of these corresponds to the Group object.

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Main()
   {
      string pattern = @"(\b(\w+?)[,:;]?\s?)+[?.!]";
      string input = "This is one sentence. This is a second sentence.";

      Match match = Regex.Match(input, pattern);
      Console.WriteLine("Match: " + match.Value);
      int groupCtr = 0;
      foreach (Group group in match.Groups)
      {
         groupCtr++;
         Console.WriteLine("   Group {0}: '{1}'", groupCtr, group.Value);
         int captureCtr = 0;
         foreach (Capture capture in group.Captures)
         {
            captureCtr++;
            Console.WriteLine("      Capture {0}: '{1}'", captureCtr, capture.Value);
         }
      }   
   }
}
// The example displays the following output:
//       Match: This is one sentence.
//          Group 1: 'This is one sentence.'
//             Capture 1: 'This is one sentence.'
//          Group 2: 'sentence'
//             Capture 1: 'This '
//             Capture 2: 'is '
//             Capture 3: 'one '
//             Capture 4: 'sentence'
//          Group 3: 'sentence'
//             Capture 1: 'This'
//             Capture 2: 'is'
//             Capture 3: 'one'
//             Capture 4: 'sentence'
Imports System.Text.RegularExpressions

Module Example
   Public Sub Main()
      Dim pattern As String = "(\b(\w+?)[,:;]?\s?)+[?.!]"
      Dim input As String = "This is one sentence. This is a second sentence."

      Dim match As Match = Regex.Match(input, pattern)
      Console.WriteLine("Match: " + match.Value)
      Dim groupCtr As Integer = 0
      For Each group As Group In match.Groups
         groupCtr += 1
         Console.WriteLine("   Group {0}: '{1}'", groupCtr, group.Value)
         Dim captureCtr As Integer = 0
         For Each capture As Capture In group.Captures
            captureCtr += 1
            Console.WriteLine("      Capture {0}: '{1}'", captureCtr, capture.Value)
         Next
      Next   
   End Sub
End Module
' The example displays the following output:
'       Match: This is one sentence.
'          Group 1: 'This is one sentence.'
'             Capture 1: 'This is one sentence.'
'          Group 2: 'sentence'
'             Capture 1: 'This '
'             Capture 2: 'is '
'             Capture 3: 'one '
'             Capture 4: 'sentence'
'          Group 3: 'sentence'
'             Capture 1: 'This'
'             Capture 2: 'is'
'             Capture 3: 'one'
'             Capture 4: 'sentence'

Properties

Captures

Gets a collection of all the captures matched by the capturing group, in innermost-leftmost-first order (or innermost-rightmost-first order if the regular expression is modified with the RightToLeft option). The collection may have zero or more items.

Name

Returns the name of the capturing group representing by the current instance.

Success

Gets a value indicating whether the match is successful.

Methods

Synchronized(Group)

Returns a Group object equivalent to the one supplied that is safe to share between multiple threads.