In this article, we are going to learn what is the difference between Select and SelectMany.
What is select?
A Select operator is used to select values from the collection.
What is SelectMany?
A SelectMany operator is used to select values from the collection of collection.
The Select operator returns one result value for every source value, while SelectMany returns a single result that contains a concatenated value for every source value. Actually, SelectMany operator flatten IEnumerable<IEnumerable<T>> to IEnumerable<T>.
Let us understand with the help of an example.
using System;
using System.Linq;
using System.Collections.Generic;
public class Employee
{
public string Name { get; set; }
public List<string> Language { get; set; }
}
public class Program
{
public static void Main(string[] args)
{
List<Employee> employees = new List<Employee>();
Employee emp1 = new Employee { Name = "Hafeezjaha", Language = new List<string> { "Node", ".Net Core", "C++" } };
Employee emp2 = new Employee { Name = "Jaha", Language = new List<string> { "SQL Server", "C#", "ASP.NET" } };
Employee emp3 = new Employee { Name = "Shaikh", Language = new List<string> { "C#", "ASP.NET MVC", "Angular", "SQL Server" } };
employees.Add(emp1);
employees.Add(emp2);
employees.Add(emp3);
// Query using Select()
IEnumerable<List<String>> resultSelect = employees.Select(e=> e.Language);
Console.WriteLine("=========Select==========");
// Two foreach loops are required to iterate through the results
// because the query returns a collection of arrays.
foreach (List<String> languageList in resultSelect)
{
// Console.WriteLine(skillList);
foreach (string language in languageList)
{
Console.WriteLine(language);
}
Console.WriteLine();
}
// Query using SelectMany()
IEnumerable<string> resultSelectMany = employees.SelectMany(emp => emp.Language);
Console.WriteLine("============ SelectMany ============");
// Only one foreach loop is required to iterate through the results
// since query returns a one-dimensional collection.
foreach (string language in resultSelectMany)
{
Console.WriteLine(language);
}
}
}
In the above example, you can see that while using Select you have to use a two loop to get LanguageList data but with the help of SelectMany, you get the same data using a single loop.
OutPut
=========Select========== Node .Net Core C++ SQL Server C# ASP.NET C# ASP.NET MVC Angular SQL Server ============ SelectMany ============ Node .Net Core C++ SQL Server C# ASP.NET C# ASP.NET MVC Angular SQL Server
That’s it.
Also check, Custom Authorization In .NET Core 5.0
