Question

I have array string format (hh.mm)
How sum ?
I use extensions:

static class SumExtensions
{
    public static String Sum<T>(this IEnumerable<T> source, Func<T, String> selector)
    {
        return source.Select(selector).Aggregate((x, y) => x + y);
    }
}

but I do not understand where parse string and sum

Answer 1

First of all, you need to convert the string to the TimeSpan representation.
It is necessary because the TimeSpan representation allows to perform arithmetic operations for time intervals.

string[] timeSpanStrings = new[]
    {
        "01.00", "02.00"
    };

var timeSpans = timeSpanStrings.Select(t => TimeSpan.ParseExact(t, @"hh\.mm", CultureInfo.InvariantCulture));
var sumTimeSpan = timeSpans.Aggregate((t1, t2) => t1.Add(t2));

The variable sumTimeSpan contains the result.