asp.net - How Get All duplicate record using linq -

in project i'm having critical problem: have collection of employees in collection. of employees have same lname:

public class employee {     public int id { get; set; }     public string fname { get; set; }     public string mname { get; set; }     public string lname { get; set; }     public datetime dob { get; set; }     public char gender { get; set; } }  public class myclass {     public list<employee> getall()     {         list<employee> emplist = new list<employee>();         emplist.add(new employee()         {             id = 1,             fname = "john",             mname = "",             lname = "shields",             dob = datetime.parse("12/11/1971"),             gender = 'm'         });         emplist.add(new employee()         {             id = 2,             fname = "mary",             mname = "matthew",             lname = "jacobs",             dob = datetime.parse("01/17/1961"),             gender = 'f'         });         emplist.add(new employee()         {             id = 3,             fname = "amber",             mname = "carl",             lname = "agar",             dob = datetime.parse("12/23/1971"),             gender = 'm'         });         emplist.add(new employee()         {             id = 4,             fname = "kathy",             mname = "",             lname = "foxsss",             dob = datetime.parse("11/15/1976"),             gender = 'f'         });         emplist.add(new employee()         {             id = 5,             fname = "lena",             mname = "ashco",             lname = "bilton",             dob = datetime.parse("05/11/1978"),             gender = 'f'         });         emplist.add(new employee()         {             id = 6,             fname = "susanne",             mname = "",             lname = "buck",             dob = datetime.parse("03/7/1965"),             gender = 'f'         });         emplist.add(new employee()         {             id = 7,             fname = "jim",             mname = "",             lname = "hooks",             dob = datetime.parse("09/11/1972"),             gender = 'm'         });         emplist.add(new employee()         {             id = 8,             fname = "jane",             mname = "g",             lname = "hooks",             dob = datetime.parse("12/11/1972"),             gender = 'f'         });         emplist.add(new employee()         {             id = 9,             fname = "robert",             mname = "",             lname = "fox",             dob = datetime.parse("06/28/1964"),             gender = 'm'         });         emplist.add(new employee()         {             id = 10,             fname = "cindy",             mname = "preston",             lname = "fox",             dob = datetime.parse("01/11/1978"),             gender = 'm'         });          return emplist;     } } 

how can duplicate records (based on lname) collection using linq?

it's not clear, looks you're looking following:

var duplicates = getall().groupby(x => x.lname)                          .where(g => g.count() > 1)                          .selectmany(g => g)                          .tolist() 

it groups element lname, takes groups have more 1 element , returns them list.

duplicates list<employee>.

you can make bit better using todictionary instead of tolist:

var duplicates = getall().groupby(x => x.lname)                          .where(g => g.count() > 1)                          .todictionary(g = > g.key, g.tolist()); 

it dictionary<string, list<employee>>, lname dictionary key, , list of items given lname value.