c# - Linq - group each class -

i need removing duplicates form emailaddresses list. need add code group emailaddresses within emailaddresses class. sql returning duplicate email addresses because of different telephone numbers. suggestions? thanks.

here code: 1. classes

public class student {     public string studentid { get; set; }     public string gender { get; set; }       public list<emailaddresses> emailaddresses { get; set; } }  public class emailaddresses {     public string emailaddress { get; set; }     } 

2. data coming sql query

studentid   emailaddresses  ispreferred number  telephonetype                                                                                                123456789   maryjoe@gmail.com   false   5556565 present evening phone                                                                                                123456789   maryjoe@gmail.com   false   8885566 permanent day phone                                                                                              123456789   mary.joe@cuu.edu    true    5556565 present evening phone                                                                                                123456789   mary.joe@cuu.edu    true    8885566 permanent day phone                                                                                              456789123   dh@mycollege.edu    true    7513150 business day phone                                                                                               456789123   donna.hill@cu.edu   true    4123300 present day phone                                                                                                456789123   donna.hill@cu.edu   false   4123300 present day phone 

3. code

public list<student> getstudentdata() {     list<student> datastudent;     using (idbconnection connection = repositoryhelper.openconnection())     {         datastudent = connection.query<dynamic>(             "mystoredprocedure",              commandtype: commandtype.storedprocedure)                 .groupby(x => x.studentid)                 .select(x => new student                      {                          studentid = x.first().studentid,                          gender = x.first().gender,                         emailaddresses = x.select(ea => new emailaddresses                              {                                  emailaddress = ea.emailaddresses                              }).tolist()                     }).tolist();          return datastudent;     } } 

while preferable filter out duplicates before returning, increases complexity of code. if result set small, memory , cpu overhead of filtering after you've returned data may suffer-able , results need. can use custom iequalitycomparer check distinct results , create new emailaddresses list on each student record contains distinct email addresses.

public list<student> getstudentdata() {     list<student> datastudent;     using (idbconnection connection = repositoryhelper.openconnection())     {         datastudent = connection.query<dynamic>(             "mystoredprocedure",              commandtype: commandtype.storedprocedure)                 .groupby(x => x.studentid)                 .select(x => new student                      {                          studentid = x.first().studentid,                          gender = x.first().gender,                         emailaddresses = x.select(ea => new emailaddresses                              {                                  emailaddress = ea.emailaddresses                              }).tolist()                     }).tolist();          datastudent.foreach(x => x.emailaddresses = x.emailaddresses             .distinct(new studentemailequalitycomparer()).tolist());          return datastudent;     } }  public class studentemailequalitycomparer : iequalitycomparer<emailaddresses> {      public bool equals(emailaddresses x, emailaddresses y)     {         return x.emailaddress.equals(y.emailaddress);     }      public int gethashcode(emailaddresses obj)     {         return obj.emailaddress.gethashcode();     } }