Using LINQ to group a list of objects

Question

I have an object   public class Customer       public int ID   get  set        public string Name   get  set        public int GroupID   get  set        I return a list that may look like the following   List lt Customer gt  CustomerList   new List lt Customer gt     CustomerList Add  new Customer   ID   1  Name    One   GroupID   1      CustomerList Add  new Customer   ID   2  Name    Two   GroupID   1      CustomerList Add  new Customer   ID   3  Name    Three   GroupID   2      CustomerList Add  new Customer   ID   4  Name    Four   GroupID   1      CustomerList Add  new Customer   ID   5  Name    Five   GroupID   3      CustomerList Add  new Customer   ID   6  Name    Six   GroupID   3        I want to return a linq query which will look like  CustomerList   GroupID  1     UserID   1  UserName    UserOne   GroupID   1     UserID   2  UserName    UserTwo   GroupID   1     UserID   4  UserName    UserFour   GroupID   1   GroupID  2     UserID   3  UserName    UserThree   GroupID   2   GroupID  3     UserID   5  UserName    UserFive   GroupID   3     UserID   6  UserName    UserSix     I tried from  Using Linq to group a list of objects into a new grouped list of list of objects  code  var groupedCustomerList   CustomerList    GroupBy u   gt  u GroupID     Select grp   gt  grp ToList       ToList      works but does not give the desired output

User · Answer

is this what you want   var grouped   CustomerList GroupBy m   gt  m GroupID  Select  n    gt  new   GroupId   n Key  Items   n ToList

User · Answer

var groupedCustomerList   CustomerList                           GroupBy u   gt  u GroupID  u  gt                                                           u Name    User    u Name                                                          return u                                                           key g   gt g ToList                              ToList      If you don t want to change the original data  you should add some method  kind of clone and modify  to your class like this   public class Customer     public int ID   get  set      public string Name   get  set      public int GroupID   get  set      public Customer CloneWithNamePrepend string prepend       return new Customer              ID   this ID            Name   prepend   this Name            GroupID   this GroupID                     Then var groupedCustomerList   CustomerList                           GroupBy u   gt  u GroupID  u  gt u CloneWithNamePrepend  User     key g   gt g ToList                              ToList      I think you may want to display the Customer differently without modifying the original data  If so you should design your class Customer differently  like this   public class Customer     public int ID   get  set      public string Name   get  set      public int GroupID   get  set      public string Prefix  get set     public string FullName       get   return Prefix   Name                       then to display the fullname  just get the customer FullName     You can also try adding some override of ToString   to your class  var groupedCustomerList   CustomerList                           GroupBy u   gt   u Prefix  User   return u GroupID      key g   gt g ToList                              ToList

User · Answer

The desired result can be obtained using IGrouping  which represents a collection of objects that have a common key in this case a GroupID   var newCustomerList   CustomerList GroupBy u   gt  u GroupID                                                     Select group   gt  new   GroupID   group Key  Customers   group ToList                                                         ToList

User · Answer

var groupedCustomerList   CustomerList GroupBy u   gt  u GroupID                                         Select grp   gt new   GroupID  grp Key  CustomerList   grp ToList                                            ToList

User · Answer

var result   from cx in CustomerList          group cx by cx GroupID into cxGroup      orderby cxGroup Key      select cxGroup    foreach  var cxGroup in result     Console WriteLine String Format  GroupID    0    cxGroup Key       foreach  var cx in cxGroup         Console WriteLine String Format   tUserID    0   UserName    1   GroupID    2           new object     cx ID  cx Name  cx GroupID

[c#] Using LINQ to group a list of objects

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