Linq group by DateTime / intervals

Question

I've the following query

 var x = from t in v
                    group t by t.Time.Year + "-" t.Time.Month + "-" + 
                      t.Time.Day + " " t.Time.Hour + ":" + t.Time.Minute into g
                    select new { Tag = g.Key, Frequency = g.Count() };

t.Time is a DateTime. The above smells a bit i.m.o. Are there any clean way to group by intervals based on DateTimes ?

Edit: What I don't quite like about this is the string fiddling and producing a string. Ideally I'd like to produce a DateTime out of the group, not a string.

Answer 1

What about this:

DateTime[] v = new DateTime[]
{
    new DateTime(2010, 01, 01, 01, 01, 00, 100),
    new DateTime(2010, 01, 01, 01, 01, 30, 200),
    new DateTime(2010, 01, 01, 02, 01, 00, 300),
    new DateTime(2010, 01, 01, 03, 01, 45, 400)
};

var x = from t in v
        //group t by t.ToString("yyyy-MM-dd HH:mm") into g
        group t by t.AddSeconds(-t.TimeOfDay.TotalSeconds % 60) into g
        select new { Tag = g.Key, Frequency = g.Count() };

EDIT: changed to .AddSeconds, per @Colin suggestion

Answer 2

something like

group t by t.AddSeconds(60- t.Time.Seconds) // rounds to nearest minute

Answer 3

Seems what I really wanted was

group t by
 new DateTime(t.Time.Year,t.Time.Month,t.Time.Day ,t.Time.Hour,t.Time.Minute,0) 
into g

None of the suggestiions involving Add/Subtract works for me, even if I also set the miliseconds to +.

dateTime.ToString("yyyy-MM-dd HH:mm") is a nice alternative to the strinc concatenation if I need a string though.

Answer 4

There are 600,000,000 ticks in a minute, so you could do something like this in order to group by the nearest minute:

var x = from t in v
        group t by new DateTime(t.Time.Ticks - (t.Time.Ticks % 600000000)) into g
        select new { Tag = g.Key, Frequency = g.Count() };

Answer 5

var x = from t in v
group t by t.Time.Date.AddMinutes((Int32)t.Time.TimeOfDay.TotalMinutes) into g
   select new { Tag = g.Key, Frequency = g.Count() };