public void GroupBy_Concert_Limit_Person_Id()
{
PersonIdentifierGroupComparer comparer = new PersonIdentifierGroupComparer();
var concertGroups = Concerts.ConcertGroup(comparer);
foreach (IGrouping <int, Concert> concertGroup in concertGroups)
{
Debug.WriteLine($"Concerts of person id {(comparer.IsInLimit(concertGroup.Key) ? "under 3" : "3 and over")} : ");
foreach (Concert concert in concertGroup)
{
Debug.WriteLine($"Number of concerts: {concert.ConcertCount}, in the year of {concert.Year} by singer {concert.PersonId}.");
}
}
}
ConcertGroup(this IEnumerable <Concert> sender, PersonIdentifierGroupComparer comparer) => sender.GroupBy(c => c.PersonId, comparer);
