Duplicate Data in ASP>NET

http://stackoverflow.com/questions/3446442/remove-duplicate-based-on-column-value-linq

List<Employee> employees = new List<Employee>()
{
    new Employee{Id =1,Name="AAAAA"}
    , new Employee{Id =2,Name="BBBBB"}
    , new Employee{Id =3,Name="AAAAA"}
    , new Employee{Id =4,Name="CCCCC"}
    , new Employee{Id =5,Name="AAAAA"}
};

List<Employee> duplicateEmployees = employees.Except(employees.GroupBy(i => i.Name)
                                             .Select(ss => ss.FirstOrDefault()))
                                            .ToList();

https://msdn.microsoft.com/en-us/library/bb348436(v=vs.110).aspx

Product[] products = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 }, 
                       new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "lemon", Code = 12 } };

//Exclude duplicates.

IEnumerable<Product> noduplicates =
    products.Distinct();

foreach (var product in noduplicates)
    Console.WriteLine(product.Name + " " + product.Code);

/*
    This code produces the following output:
    apple 9 
    orange 4
    lemon 12
*/

http://stackoverflow.com/questions/30421153/remove-duplicate-records-using-linq

You can use GroupBy and then Select with OrderByDescending to order the dates.
public class Item 
{
    public int Aid {get;set;}

    public int Bid {get;set;}

    public DateTime CDate {get;set;}
}

void Main()
{
    var items = new List<Item>
    {
        new Item { Aid = 1, Bid = 2, CDate = new DateTime(2015, 5, 24)},
        new Item { Aid = 3, Bid = 6, CDate = new DateTime(2015, 5, 24)},
        new Item { Aid = 1, Bid = 2, CDate = new DateTime(2015, 5, 23)},        
    };

    var result =  items.GroupBy(i => i.Aid)
                  .Select(group => 
                        new { Key = group.Key,
                              Items = group.OrderByDescending(x => x.CDate) })
                  .Select (g => g.Items.First());


    result.Dump();
}

http://stackoverflow.com/questions/3446442/remove-duplicate-based-on-column-value-linq

Okay, if you don't care which employee is removed, you could try something like:
var result = query.GroupBy(x => x.EmployeeId)
                  .Select(group => group.First());

You haven't specified whether this is in LINQ to SQL, LINQ to Objects or something else... I don't know what the SQL translation of this would be. If you're dealing with a relatively small amount of data you could always force this last bit to be in-process:
var result = query.AsEnumerable()
                  .GroupBy(x => x.EmployeeId)
                  .Select(group => group.First());

At that point you could actually use MoreLINQ which has a handy DistinctBy method:
var result = query.AsEnumerable()
                  .DistinctBy(x => x.EmployeeId);