How to delete duplicates in an output list?

Question

I am pretty new to c# and am coding an assignment that is to output years, courses taken each year, and the students who have taken that class. I am taking this information from an external file that includes all the information. When I try to output the values, I get one class that's taken in 2 different years, but the students are showing up for both years when they have only taken it once.

foreach (Years y in year2)
{
    Console.WriteLine("Year: {0}", y.gYear);

    foreach (Classes c in class2)
    {
        if (y.gYear == c.gYear)
        {
            Console.WriteLine("Class: {0}", c.gCourse);

            foreach (Grades g in grade2)
            {
                if (g.gCourse == c.gCourse )
                {
                    //Console.WriteLine("Student: {0}", g.sID);

                    foreach (Students s in stud2)
                    {
                        if (s.sID == g.sID)
                        {
                            Console.WriteLine("{0} {1} | Grade: {2}", s.sFirst, s.sLast, g.gGrade);
                        }
                    }
                }
            }   
        }
    }

    Console.WriteLine("");
}

Also, I want to delete duplicate classes. Say for the first year, which is 2015, there are 2 students taking the same course. So in the output, it states the course twice and under each course is both of the students.

Output I am getting:

Have you considered using linq? Or is it a requirement to go without it? Also if it's some sort of a test I would suggest using for loop instead of foreach because it works faster. — Gleb
– Gleb, Commented Dec 17, 2019 at 5:17
@Gleb I have Linq in using on my code, but it's not being used. How could I use it? — swim247
– swim247, Commented Dec 17, 2019 at 5:26
could you demonstrate the input file too? I can't understand the problem yet. — Peyman Mahdavi
– Peyman Mahdavi, Commented Dec 17, 2019 at 6:08

StuartLC · Accepted Answer · 2019-12-17 08:19:00Z

You haven't shown your data classes, but with virtual certainty, you've missed out a join condition on Grade to Year (i.e. Grades are the 'fact' field value intersecting between Year, Course and Student).

Without this extra join condition, you are getting the cartesian product of Student Grade 'repeated' for each year that the Course was held, with the only restriction being that the student must have done that course at least once, and that's why you are seeing the same students repeating in every year that the same Course is held.

Your Grades class should look like so:

class Grades
{
  public string gCourse {get; set; }
  public int sId {get; set; }
  public int gGrade {get; set; }
  public int gYear {get; set; } // <<< Use this
}

You can address the unwanted repetition by adding in the extra join condition, like so:

// ... Outer loops
foreach (Grades g in grade2)
{
    if (g.gCourse == c.gCourse && g.gYear == y.gYear) // << Additional Join condition
    {
        foreach (Students s in stud2)
        {
            if (s.sId == g.sId)
            {
                Console.WriteLine("{0} {1} | Grade: {2}", s.sFirst, s.sLast, g.gGrade);
            }
        }
    }
}

Collectives™ on Stack Overflow

How to delete duplicates in an output list?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related