Difference between Select and SelectMany in LINQ

Select and SelectMany are projection operator and Select method is used to select a

value from collection and SelectMany method is used to select value from multiple

collection. 

In below example, we will see that Select will returns the collection of Player object and to read Player Name, we need one more For Each loop to read the Player object and

SelectMany will flatten the list into a single list of Players, so we need only one for-each

loop to get player name.

C# Example : 

List<Team> teams = new List<Team>();

Team team1 = new Team {

             Name = "USA",

             Players = new List<Player> {

                                     new Player {  PlayerName = "John" },

                                     new Player { PlayerName = "Peter" },

                                     new Player { PlayerName = "Steve" }

             } };

Team team2 = new Team

         {

             Name = "AUS",

             Players = new List<Player> {

                    new Player {  PlayerName = "Ricky" },

                    new Player { PlayerName = "McGraw" },

                    new Player { PlayerName = "Donald" }

             }

         };

teams.Add(team1);

teams.Add(team2);

Select : 

by using Select query. We need two for-each loop to retrieve the player name from a

team collection of arrays, because Select returns a collection of arrays.

C# Example : 

var resultSelect = teams.Select(e => e.Players);

foreach (var playerList in resultSelect)

         {

                foreach (var player in playerList)

             {                      Console.WriteLine(player.PlayerName);

             }

                Console.WriteLine();

         }

Output:

John

Peter

Steve

Ricky

McGraw

Donald

SelectMany: 

By using SelectMany query, we only need one for each loop to retrieve the player name

from team collection of array and SelectMany returns a one dimensional collection.

C# Example : 

     

      var resultSelectMany = teams.SelectMany(emp => emp.Players);

      foreach (var player in resultSelectMany)

         {

                Console.WriteLine(player.PlayerName);

         }

            Console.ReadKey();

     }

Output:

John

Peter

Steve

Ricky

McGraw

Donald

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