Question

If i have a time period, lets say DateFrom and DateTo and I have a list of Dates, These dates will be the split dates. For example:

DateTime dateFrom = new DateTime(2012, 1, 1);
DateTime dateTo = new DateTime(2012, 12, 31);

List<DateTime> splitDates = new List<DateTime>
    {
        new DateTime(2012,2,1),
        new DateTime(2012,5,1),
        new DateTime(2012,7,1),
        new DateTime(2012,11,1),
    };

List<Tuple<DateTime, DateTime>> periods = SplitDatePeriod(dateFrom, dateTo, splitDates);

I want the result to be a list of periods, so for the previous example the result should be:

(01/01/2012 - 01/02/2012)
(02/02/2012 - 01/05/2012)
(02/05/2012 - 01/07/2012)
(02/07/2012 - 01/11/2012)
(02/11/2012 - 31/12/2012)

I have already wrote a method to do that:

List<Tuple<DateTime, DateTime>> SplitDatePeriod(DateTime dateFrom, DateTime dateTo, List<DateTime> splitDates)
{
    var resultDates = new List<Tuple<DateTime, DateTime>>();

    // sort split dates
    List<DateTime> _splitDates = splitDates.OrderBy(d => d.Date).ToList();

    DateTime _curDate = dateFrom.Date;
    for (int i = 0; i <= _splitDates.Count; ++i)
    {
        DateTime d = (i < _splitDates.Count) ? _splitDates[i] : dateTo;

        // skip dates out of range
        if (d.Date < dateFrom.Date || d.Date > dateTo.Date)
            continue;

        resultDates.Add(Tuple.Create(_curDate, d));

        _curDate = d.AddDays(1);
    }
    return resultDates;
}

The Question
It looks so ugly, Is there more neat and shorter way of doing this? using Linq maybe?

Answer 1

This is one that works and takes care of some edge cases also:

var realDates = splitDates
    .Where(d => d > dateFrom && d < dateTo)
    .Concat(new List<DateTime>() {dateFrom.AddDays(-1), dateTo})
    .Select(d => d.Date)
    .Distinct()
    .OrderBy(d => d)
    .ToList();

// now we have             (start - 1) -- split1 -- split2 -- split3 -- end
// we zip it against          split1   -- split2 -- split3 --  end
// and produce       start,split1 -- split1+1,split2 -- split2+1,split3 -- split3+1,end

realDates.Zip(realDates.Skip(1), (a, b) => Tuple.Create(a.AddDays(1), b));