{"id":1921,"date":"2023-06-01T14:35:36","date_gmt":"2023-06-01T07:35:36","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1921"},"modified":"2023-06-01T14:36:17","modified_gmt":"2023-06-01T07:36:17","slug":"c-regex-groups","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-regular-expression\/c-regex-groups\/","title":{"rendered":"C# Regex Groups"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about capturing groups and how to use the C# Regex Groups property to get the matches.<\/p>\n\n\n\n

Introduction to the C# Regex Groups<\/h2>\n\n\n\n

Suppose you want to match a route that starts with posts<\/code> followed by a forward slash \/<\/code> and an id<\/code> like this:<\/p>\n\n\n

posts\/id<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
To do that, you may come up with the following regular expression pattern:<\/p>\n\n\n
posts\/\\d+<\/code><\/span><\/pre>\n\n\n
And the following program illustrates how you would use that pattern to match the route:<\/p>\n\n\n
using<\/span> System.Text.RegularExpressions;\nusing<\/span> static<\/span> System.Console;\n\n\nvar<\/span> route = \"posts\/100\"<\/span>;\nvar<\/span> pattern = @\"posts\/\\d+\"<\/span>;\n\nvar<\/span> match = Regex.Match(route, pattern);\n\nWriteLine(match.Value);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
posts\/100<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The pattern posts\/\\d+<\/code> matches the posts\/<\/code> characters and is followed by one or more digits. It returns the result as expected.<\/p>\n\n\n\n
Now, you want to extract the id from the route, which is 100 in this case. To do that, you can use something called capturing group<\/strong> in regular expressions. <\/p>\n\n\n\n
By definition, a capturing group allows you to capture a portion of the matched text. To create a capturing group, you define a subpattern within the overall pattern and closed it within parentheses.<\/p>\n\n\n\n
In our example, we can create a subpattern like this:<\/p>\n\n\n
posts\/(\\d+)<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
This (\\d+)<\/code> is a capturing group and \\d+<\/code> is a subpattern. <\/p>\n\n\n\n
If the matches are found, you can access the groups via the Groups<\/code> property of the Match<\/code> object. The type of Groups<\/code> is the GroupCollection<\/code> type which is a collection of Group<\/code> objects.<\/p>\n\n\n\n
The first element in the Groups<\/code> collection is the whole match which is posts\/100<\/code> in this example and the next elements are the matched text of the capturing groups.<\/p>\n\n\n\n
The following example uses the capturing group to exact the id<\/code> from the route posts\/100<\/code>:<\/p>\n\n\n
using<\/span> System.Text.RegularExpressions;\nusing<\/span> static<\/span> System.Console;\n\nvar<\/span> route = \"posts\/100\"<\/span>;\nvar<\/span> pattern = @\"posts\/(\\d+)\"<\/span>;\n\nvar<\/span> match = Regex.Match(route, pattern);\n\nif<\/span> (match.Success)\n{\n    foreach<\/span> (var<\/span> group<\/span> in<\/span> match.Groups)\n    {\n        WriteLine(group<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
posts\/100<\/span>\n100<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
A regular expression may contain multiple capturing groups. For example:<\/p>\n\n\n
using<\/span> System.Text.RegularExpressions;\nusing<\/span> static<\/span> System.Console;\n\n\n\/\/ posts\/year\/month\/date format<\/span>\nvar<\/span> route = \"posts\/2023\/12\/31\"<\/span>;\n\nvar<\/span> pattern = @\"posts\/(\\d{4})\/(\\d{2})\/(\\d{2})\"<\/span>;\n\nvar<\/span> match = Regex.Match(route, pattern);\n\nif<\/span> (match.Success)\n{\n    foreach<\/span> (var<\/span> group<\/span> in<\/span> match.Groups)\n    {\n        WriteLine(group<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
posts\/2023<\/span>\/12<\/span>\/31<\/span>\n2023<\/span>\n12<\/span>\n31<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we have three capturing groups for year, month, and date in the route. The output shows four groups, which include the whole match.<\/p>\n\n\n\n
Named capturing groups<\/h2>\n\n\n\n
By using the Groups<\/code> property, you can iterate the groups or access a group by index. For example, the  Groups[1]<\/code> should return the year which is 2023<\/code>:<\/p>\n\n\n
using System;\r\nusing System.Text.RegularExpressions;\r\nusing static<\/span> System.Console;\r\n\r\n\r\n\/\/ posts\/year\/month\/date format<\/span>\r\nvar<\/span> route = \"posts\/2023\/12\/31\"<\/span>;\r\n\r\nvar<\/span> pattern = @\"posts\/(\\d{4})\/(\\d{2})\/(\\d{2})\"<\/span>;\r\n\r\nvar<\/span> match = Regex.Match(route, pattern);\r\n\r\nif<\/span> (match.Success && match.Groups.Count == 4<\/span>)\r\n{\r\n    var<\/span> year = match.Groups[1<\/span>];\r\n    var<\/span> month = match.Groups[2<\/span>];\r\n    var<\/span> day = match.Groups[3<\/span>];\r\n    WriteLine($\"{year}\/{month}\/{day}\"<\/span>);\r\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
It’s more explicit to assign a name to each capturing in the regular expression so that we can access each group by name rather than by index.<\/p>\n\n\n\n
To do that, you can use the following syntax:<\/p>\n\n\n
(?<name>rule)<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this syntax:<\/p>\n\n\n\n
    \n
  • The ()<\/code> denotes a capturing group.<\/li>\n\n\n\n
  • The ?<name><\/code> specifies the capturing group’s name.<\/li>\n\n\n\n
  • The rule<\/code> is a subpattern.<\/li>\n<\/ul>\n\n\n\n
    To access the matched value, you look it up in the Groups<\/code> property by group name like this:<\/p>\n\n\n
    Groups[\"name\"<\/span>]<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    For example:<\/p>\n\n\n
    using<\/span> System.Text.RegularExpressions;\nusing<\/span> static<\/span> System.Console;\n\n\n\/\/ posts\/year\/month\/date format<\/span>\nvar<\/span> route = \"posts\/2023\/12\/31\"<\/span>;\n\nvar<\/span> pattern = @\"posts\/(?<year>\\d{4})\/(?<month>\\d{2})\/(?<day>\\d{2})\"<\/span>;\n\nvar<\/span> match = Regex.Match(route, pattern);\n\nif<\/span> (match.Success)\n{\n    var<\/span> year = match.Groups[\"year\"<\/span>];\n    var<\/span> month = match.Groups[\"month\"<\/span>];\n    var<\/span> day = match.Groups[\"day\"<\/span>];\n    WriteLine($\"{year}<\/span>\/{month}<\/span>\/{day}<\/span>\"<\/span>);\n\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    2023<\/span>\/12<\/span>\/31<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Summary<\/h2>\n\n\n\n
      \n
    • Place a pattern inside the parentheses ()<\/code> to create a capturing group.<\/li>\n\n\n\n
    • Use the Match.Groups<\/code> property to access the groups. The first group is the whole match and the next ones are the matched groups.<\/li>\n\n\n\n
    • Use the (?<name>rule)<\/code> syntax to assign a name<\/code> to a capturing group and access its matched value using Groups[\"name\"]<\/code>.<\/li>\n<\/ul>\n
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      Was this tutorial helpful ?<\/div>\n\t\t
      \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
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