How to not print duplicates in a data grid view using LINQ

Question

I have a table called TIME and there are multiple students in it. Sometimes, student A will have more than one entry in TIME. How do I print just the latest record for student A?

Answer 1

You want latest student A?.. Then may be you need something like this:

dataGridView.DataSource = students.GroupBy(s => s.Name).
Select(i => i.OrderByDescending(s => s.DateChanged).First());

I assume here that you can sort them by some parameter(i used DateChanged here..May be you have some incremental primary key or smth).

Answer 2

This sample uses Distinct to remove duplicate elements in a sequence of factors of 300.

public void Linq46()
{
    int[] factorsOf300 = { 2, 2, 3, 5, 5 };

    var uniqueFactors = factorsOf300.Distinct();

    Console.WriteLine("Prime factors of 300:");
    foreach (var f in uniqueFactors)
    {
        Console.WriteLine(f);
    }
}

Result

Prime factors of 300: 2 3 5
See: http://msdn.microsoft.com/en-us/vcsharp/aa336761.aspx#distinct1

Answer 3

void Main ()
{

    var rows = new [] {
        new Student { Name = "A", Timestamp = DateTime.Now.AddHours (-1) },
        new Student { Name = "A", Timestamp = DateTime.Now.AddHours (-3) },
        new Student { Name = "B", Timestamp = DateTime.Now.AddHours (4) },
        new Student { Name = "B", Timestamp = DateTime.Now.AddHours (1) },
        new Student { Name = "B", Timestamp = DateTime.Now }
    };

    var recentRows = from row in rows
        group row by row.Name into studentRows
        select studentRows.OrderByDescending (sr => sr.Timestamp).First ();

    Console.WriteLine (recentRows);
}


class Student {
    public string Name { get; set; }
    public DateTime Timestamp { get; set; }
}

Answer 4

You have to group the records by student entry time.

from r in StudentRecords
group r by r.StudentId into g
select new { StudentId = g.Key, MostRecentEntry = g.Max(e => e.EntryTime)}

since I don't know your schema, I've used some arbitrary names