locked
What is the difference between select and SelectMany RRS feed

  • Question

  • please explain when to use SelectMany instead of select with a example code.
    Thursday, December 14, 2017 6:04 PM

Answers

  • Hi Sudip_inn,

    >>please explain when to use SelectMany instead of select with a example code.

    Select operator is used to select value from a collection and SelectMany operator is used to select values from a collection of collection i.e. nested collection.

    Select operator produce one result value for every source value while SelectMany produce a single result that contains a concatenated value for every source value. Actually, SelectMany operator flatten IEnumerable<IEnumerable<T>> to IEnumrable<T> for example. list of list to list.

    Here is a simple console app for your reference.

    public class Employee
    {
    public string Name { get; set; }
    public List<string> Skills { get; set; }
    }

    class Program { static void Main(string[] args) { List<Employee> employees = new List<Employee>(); Employee emp1 = new Employee { Name = "Deepak", Skills = new List<string> { "C", "C++", "Java" } }; Employee emp2 = new Employee { Name = "Karan", Skills = new List<string> { "SQL Server", "C#", "ASP.NET" } }; Employee emp3 = new Employee { Name = "Lalit", Skills = new List<string> { "C#", "ASP.NET MVC", "Windows Azure", "SQL Server" } }; employees.Add(emp1); employees.Add(emp2); employees.Add(emp3); // Query using Select() IEnumerable<List<String>> resultSelect = employees.Select(e=> e.Skills); Console.WriteLine("----------------- Select ---------------------"); // Two foreach loops are required to iterate through the results // because the query returns a collection of arrays. foreach (List<String> skillList in resultSelect) { foreach (string skill in skillList) { Console.WriteLine(skill); } Console.WriteLine(); } // Query using SelectMany() IEnumerable<string> resultSelectMany = employees.SelectMany(emp => emp.Skills); Console.WriteLine("----------------- SelectMany ------------------"); // Only one foreach loop is required to iterate through the results // since query returns a one-dimensional collection. foreach (string skill in resultSelectMany) { Console.WriteLine(skill); } Console.ReadKey(); } }

    For more information, please refer to:

    https://stackoverflow.com/questions/958949/difference-between-select-and-selectmany

    Best regards,

    Zhanglong Wu


    MSDN Community Support
    Please remember to click "Mark as Answer" the responses that resolved your issue, and to click "Unmark as Answer" if not. This can be beneficial to other community members reading this thread. If you have any compliments or complaints to MSDN Support, feel free to contact MSDNFSF@microsoft.com.


    Friday, December 15, 2017 2:55 AM