{"id":1083,"date":"2023-03-19T10:05:32","date_gmt":"2023-03-19T03:05:32","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1083"},"modified":"2023-06-26T15:22:53","modified_gmt":"2023-06-26T08:22:53","slug":"linq-thenby","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-linq\/linq-thenby\/","title":{"rendered":"LINQ ThenBy"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the LINQ ThenBy()<\/code> method to sort a sequence in ascending order based on a secondary key.<\/p>\n\n\n\n

Introduction to the LINQ ThenBy() method<\/h2>\n\n\n\n

The LINQ ThenBy()<\/code> method sorts a sequence in ascending order based on a secondary key after the sequence has been sorted by a primary key using the OrderBy()<\/a><\/code> or OrderByDescending()<\/a><\/code> method:<\/p>\n\n\n

public<\/span> static<\/span> IOrderedEnumerable<TSource> ThenBy<TSource, TKey> (\n    this<\/span> IOrderedEnumerable<TSource> source, \n    Func<TSource, TKey> keySelector\n);<\/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
  • TSource<\/code> is the type of elements in the source<\/code> sequence.<\/li>\n\n\n\n
  • TKey<\/code> is the type of sort key.<\/li>\n\n\n\n
  • source<\/code> is the input sequence to sort.<\/li>\n\n\n\n
  • keySelector<\/code> is a function that selects a key to sort the source<\/code> sequence.<\/li>\n<\/ul>\n\n\n\n
    The ThenBy()<\/code> method returns a new sequence sorted by a key in ascending order with the type of IOrderedEnumerable<TSource><\/code>.<\/p>\n\n\n\n
    If the source<\/code> or keySelector<\/code> is null, the method ThenBy()<\/code> method will throw an ArgumentNullException<\/code>.<\/p>\n\n\n\n
    LINQ ThenBy() method example<\/h2>\n\n\n\n
    The following example use the OrderBy()<\/code> to sort a list of employees by department alphabetically first and then use the ThenBy()<\/code> method to sort the employees in each department by Salary<\/code> from low to high:<\/p>\n\n\n
    using<\/span> static<\/span> System.Console;\n\nclass<\/span> Employee<\/span>\n{\n    public<\/span> string<\/span>? Name { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span>? Department { get<\/span>; set<\/span>; }\n    public<\/span> int<\/span> Salary { get<\/span>; set<\/span>; }\n}\nclass<\/span> Program<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(<\/span>)<\/span>\n    {\n        var<\/span> employees = new<\/span> List<Employee>()\n        {\n            new<\/span> Employee { Name = \"John\"<\/span>, Department = \"HR\"<\/span>, Salary = 50000<\/span> },\n            new<\/span> Employee { Name = \"Jane\"<\/span>, Department = \"IT\"<\/span>, Salary = 60000<\/span> },\n            new<\/span> Employee { Name = \"Bob\"<\/span>, Department = \"HR\"<\/span>, Salary = 45000<\/span> },\n            new<\/span> Employee { Name = \"Sara\"<\/span>, Department = \"IT\"<\/span>, Salary = 55000<\/span> },\n            new<\/span> Employee { Name = \"Tom\"<\/span>, Department = \"IT\"<\/span>, Salary = 65000<\/span> }\n        };\n\n        var<\/span> results = employees.OrderBy(e => e.Department).ThenBy(e => e.Salary);\n\n        foreach<\/span> (var<\/span> e in<\/span> results)\n        {\n            WriteLine($\"{e.Department}<\/span> - {e.Name}<\/span> - {e.Salary:C}<\/span>\"<\/span>);\n        }\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    HR - Bob - $45,000.00\nHR - John - $50,000.00\nIT - Sara - $55,000.00\nIT - Jane - $60,000.00\nIT - Tom - $65,000.00<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
    How it works.<\/p>\n\n\n\n
    First, define the Employee<\/code> class that has three properties: Name<\/code>, Department<\/code>, and Salary<\/code>:<\/p>\n\n\n
    class<\/span> Employee<\/span>\n{\n    public<\/span> string<\/span>? Name { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span>? Department { get<\/span>; set<\/span>; }\n    public<\/span> int<\/span> Salary { get<\/span>; set<\/span>; }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Second, create a new list that has five Employee<\/code> objects:<\/p>\n\n\n
    var<\/span> employees = new<\/span> List<Employee>() \n{\n    new<\/span> Employee { Name = \"John\"<\/span>, Department = \"HR\"<\/span>, Salary = 50000<\/span> },\n    new<\/span> Employee { Name = \"Jane\"<\/span>, Department = \"IT\"<\/span>, Salary = 60000<\/span> },\n    new<\/span> Employee { Name = \"Bob\"<\/span>, Department = \"HR\"<\/span>, Salary = 45000<\/span> },\n    new<\/span> Employee { Name = \"Sara\"<\/span>, Department = \"IT\"<\/span>, Salary = 55000<\/span> },\n    new<\/span> Employee { Name = \"Tom\"<\/span>, Department = \"IT\"<\/span>, Salary = 65000<\/span> }\n};<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Third, sort the Employee<\/code> objects by departments in ascending order using the OrderBy()<\/code> method and then sort the Employee<\/code> objects in each department by salary using the ThenBy()<\/code> method:<\/p>\n\n\n
    var<\/span> results = employees.OrderBy(e => e.Department)\n                       .ThenBy(e => e.Salary);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Finally, write the employees to the console using a foreach<\/code> and WriteLine()<\/code> method:<\/p>\n\n\n
    foreach<\/span> (var<\/span> e in<\/span> results)\n{\n    WriteLine($\"{e.Department}<\/span> - {e.Name}<\/span> - {e.Salary:C}<\/span>\"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Summary<\/h2>\n\n\n\n
      \n
    • Use LINQ ThenBy()<\/code> method to sort elements in a sequence in ascending order by a secondary key, after the sequence has been sorted by a primary key in ascending order using the OrderBy()<\/code> method.<\/li>\n<\/ul>\n
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