GroupCollection.Item Property (String)
Enables access to a member of the collection by string index.
Assemblies: System (in System.dll)
System.Text.RegularExpressions (in System.Text.RegularExpressions.dll)
groupName can be either the name of a capturing group that is defined by the (?<name>) element in a regular expression, or the string representation of the number of a capturing group that is defined by a grouping construct. For more information about groups in regular expressions, see Grouping Constructs in Regular Expressions.
You can retrieve the names of all the captured groups in a Regex object by calling the Regex.GetGroupNames method. You can also map the numbers of capturing groups in a regular expression to their names by calling the Regex.GroupNameFromNumber method. Individual names from the array can then be passed to the property to retrieve the captured string.
If groupname is not the name of a capturing group in the collection, or if groupname is the name of a capturing group that has not been matched in the input string, the method returns a Group object whose Group.Success property is false and whose Group.Value property is String.Empty.
The following example defines a regular expression that consists of two named groups. The first group, numbers, captures one or more consecutive digits. The second group, letter, matches a single character. Because the regular expression engine looks for zero or one occurrence of the pattern defined by the numbers group, the numbers group is not always present even if a match is successful. The example then illustrates the result when the property is used to retrieve an unmatched group, a matched group, and a group that is not defined in the regular expression. The example defines a regular expression pattern (?<numbers>\d+)*(?<letter>\w)\k<letter>, which is interpreted as shown in the following table.
Match one or more occurrence of a decimal digit. Name this the numbers capturing group. Match this pattern either zero or one time.
Match a single word character. Name this the letter capturing group.
Match the string captured by the letter capturing group.