Question

I have the following foreach loop:

List<WorkingJournal> workingJournals = new List<WorkingJournal>();
foreach (WorkRoster workRoster in workRosters)
{
    bool exists = workingJournals.Any(workingJournal => workingJournal.ServicePlan.Id == workRoster.ServicePlan.Id
                                      && workingJournal.Nurse.Id == workRoster.Nurse.Id
                                      && workingJournal.Month == workRoster.Start.Month
                                      && workingJournal.Year == workRoster.Start.Year);

    if (exists == false)
    {
                WorkingJournal workingJournal = new WorkingJournal
                {
                    ServicePlan = workRoster.ServicePlan,
                    Nurse = workRoster.Nurse,
                    Month = workRoster.Start.Month,
                    Year = workRoster.Start.Year
                };

                workingJournals.Add(workingJournal);
    }
}

I started writing:

from workRoster in workRosters
select new WorkingJournal
                {
                    ServicePlan = workRoster.ServicePlan,
                    Nurse = workRoster.Nurse,
                    Month = workRoster.Start.Month,
                    Year = workRoster.Start.Year
                };

But now I am stuck with the comparison that produces distinct WorkingJournals.
I have a feeling that a group by clause should be here but I’m not sure how it should be done.

Answer 1

If you have proper Equals and GetHashCode implementations inside your class, you can simply invoke Distinct().

var result = workRosters.Select(...).Distinct();

On the chance you do not have such implementations, you can define an IEqualityComparer<WorkingJournal> implementation. This will have you defining Equals and GetHashCode methods for the T that can then be used by a dictionary or hashset and can also be used in overloads of Distinct() in Linq.

class JournalComparer : IEqualityComparer<WorkingJournal>
{
    public bool Equals(WorkingJournal left, WorkingJournal right)
    {
         // perform your equality semantics here
    }

    public int GetHashCode(WorkingJournal obj)
    {
         // return some hash code here.
         return obj.ServicePlan.GetHashCode();
    }
}

var comparer = new JournalComparer(); // implements the interface 
var result = workRosters.Select(r => new WorkingJournal { ... }).Distinct(comparer);