CODEWITHSUNDEEP
c#linqtimespan
DreamToCode
DreamToCode

Reputation: 291

Average time from a list of start end times in linq to sql

I have a list of 

*startTime    (datetime)
*endTime      (datetime)

and need to work out the average time for everything in the list.

So I am guessing I need something like

long averageTime = 
 Convert.ToInt64(listOfStartEndTimes.Average(timeSpan => timeSpan.Ticks))

Any ideas?

Upvotes: 2

Views: 2729

Answers (3)

Matt Johnson-Pint
Matt Johnson-Pint

Reputation: 241920

The other answers are correct that you can average TimeSpan properties with simple LINQ. I prefer letting the TimeSpan class do it's work to determine precision, such as Uffe showed. But make sure you are using the correct property. .Seconds will return the remainder of seconds that don't fit into a full minute. You want the .TotalSeconds property.

Using .Ticks might be tempting, but you could easily get an OverflowException if you have a lot of values and they are spaced far enough apart from each other. My recommendation is to use one unit smaller than you need in your result. So if you care about average precision to the minute, then .TotalSeconds should work well. You can then take the result back into a TimeSpan if you like.

var sec = yourList.Select(p => p.Stop - p.Start).Average(p => p.TotalSeconds);
var avg = TimeSpan.FromSeconds(sec);

Also, since your Start and Stop values are of type DateTime, then you really need to pay attention to their .Kind. An operation like this is only guaranteed to be accurate if yourDateTime.Kind == DateTimeKind.Utc.

If they are Local kinds, then the result will be influenced by the time zone of the local computer that is running the code. If they are Unspecified, then the data may have been recorded in the context of the local time zone, or of some other time zone. If the times you are working in cover a daylight saving time transition, then your result of subtraction may be incorrect.

For example, if you are running this code in the US Pacific Time zone, and you have Local kinds of DateTime, then subtracting 2013-11-03 06:00 - 2013-11-03 00:00 would give you a TimeSpan of 6 hours. But in reality, 7 hours will have elapsed, since that is the day DST ends and the clocks repeat the hour between 1:00 and 2:00.

To avoid this problem, you should only do math with DateTime values that are in Utc, or you should use DateTimeOffset values instead.

Upvotes: 2

It'sNotALie.
It'sNotALie.

Reputation: 22814

long averageTime = listOfStartEndTimes
                       .Select(se => se.End - se.Start)
                       .Average(t => t.Ticks);

Or alternatively, with a slightly lower resolution (unix epoch date instead):

long averageTime = listOfStartEndTimes
                       .Select(se => se.End - se.Start)
                       .Average(t => (t.Ticks – 621355968000000000) / 10000000);

Upvotes: 4

Uffe
Uffe

Reputation: 2275

If you have a class

public class Time
{
    public DateTime Start;
    public DateTime Stop;

    public Time(DateTime start, DateTime stop)
    {
        this.Start = start;
        this.Stop = stop;
    }
}

That you fill with datetime values you can probably get the average with...

var avg = Times.Select(p => p.Stop - p.Start).Average(p => p.Seconds);

Where you can replace p.Seconds with whatever you would like.. Hours, minutes etc... Note: Not tested, but I think it might work

Edit: Ahh, already answered :)

Upvotes: 0

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