Question

I’m working with a list of objects in C#, each contains a DateTime property and I need to know if n of the objects happened in an hour.

Do I have to compare each of the objects? Is there a quicker way? I don’t know, can this be done with Linq?

Answer 1

You could use Where+Count:

// for example today between 12 and 13 o'clock
DateTime startHour = DateTime.ToDay.AddHours(12)
DateTime endHour = startHour.AddHours(1);
var inHour = collection.Where(o => o.DateTimeProperty >= startHour 
                                && o.DateTimeProperty <= endHour);
int count = inHour.Count();

Of course this is the same as a simple loop. But that’s the way you have to go.

You could also use GroupBy but i don’t see why you could need it.

var hourGroup = collection
   .GroupBy(o => o.DateTimeProperty.AddMinutes((-1) * o.DateTimeProperty.Minute))
   .FirstOrDefault(g => g.Key == startHour);
if(hourGroup != null)
{
    int count = hourGroup.Count();
}