How to flatten a list using LINQ C#?

Flattening a list means converting a List<List<T>> to List<T>. For example, let us consider a List<List<int>> which needs to be converted to List<int>.

The SelectMany in LINQ is used to project each element of a sequence to an IEnumerable<T> and then flatten the resulting sequences into one sequence. That means the SelectMany operator combines the records from a sequence of results and then converts it into one result.

Using SelectMany

Example

 Live Demo

using System; using System.Collections.Generic; using System.Linq; namespace DemoApplication{    public class Program{       static void Main(string[] args){          List<List<int>> listOfNumLists = new List<List<int>>{             new List<int>{                1, 2             },             new List<int>{                3, 4             }          };          var numList = listOfNumLists.SelectMany(i => i);          Console.WriteLine("Numbers in the list:");          foreach(var num in numList){             Console.WriteLine(num);          }          Console.ReadLine();       }    } }

Output

Numbers in the list: 1 2 3 4

Using Query

Example

 Live Demo

using System; using System.Collections.Generic; using System.Linq; namespace DemoApplication{    public class Program{       static void Main(string[] args){          List<List<int>> listOfNumLists = new List<List<int>>{             new List<int>{                1, 2             },             new List<int>{                3, 4             }          };          var numList = from listOfNumList in listOfNumLists          from value in listOfNumList          select value;          Console.WriteLine("Numbers in the list:");          foreach(var num in numList){             Console.WriteLine(num);          }          Console.ReadLine();       }    } }

Output

Numbers in the list: 1 2 3 4