Find average of collection of TimeSpans

I have collection of TimeSpans, they represent time spent doing a task. Now I would like to find the average time spent on that task. It should be easy but for some reason I'm not getting the correct average.

Here's my code:

private TimeSpan? GetTimeSpanAverage(List<TimeSpan> sourceList)
{
    TimeSpan total = default(TimeSpan);

    var sortedDates = sourceList.OrderBy(x => x);

    foreach (var dateTime in sortedDates)
    {
        total += dateTime;
    }
    return TimeSpan.FromMilliseconds(total.TotalMilliseconds/sortedDates.Count());
}

You can use the Average overload that takes a collection of long in parameter:

double doubleAverageTicks = sourceList.Average(timeSpan => timeSpan.Ticks);
long longAverageTicks = Convert.ToInt64(doubleAverageTicks);

return new TimeSpan(longAverageTicks);

var average = new TimeSpan(sourceList.Select(ts => ts.Ticks).Average());

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Note, your method returns a Nullable, but doesn't need to, unless you want to return null if the source list is empty, in which case just do a separate check first.

In Addition to the above answer, I would suggest you take an average on the Seconds or MilliSeconds level (depending on what you require)

sourceList.Average(timeSpan => timeSpan.ToTalMilliseconds)

Now using this value you could arrive at the new TimeSpan using

TimeSpan avg = TimeSpan.FromMilliseconds(double value here)