Find missing dates for a given range

I'm trying to find missing dates between two DateTime variables for a collection of DateTimes.

For example.

Collection
2010-01-01
2010-01-02
2010-01-开发者_如何学JAVA03
2010-01-05

DateRange
2010-01-01 -> 2010-01-06

would give me a List<DateTime> of

2010-01-04
2010-01-06

I can think of a few was of implementing this but nothing clean and simple

Any ideas?

I can think of a lot of ways of implementing this, e.g.:

DateTime[] col = { new DateTime(2010, 1, 1),
                   new DateTime(2010, 1, 2),
                   new DateTime(2010, 1, 3),
                   new DateTime(2010, 1, 5)};

var start = new DateTime(2010, 1, 1);
var end = new DateTime(2010, 1, 6);

var range = Enumerable.Range(0, (int)(end - start).TotalDays + 1)
                      .Select(i => start.AddDays(i));

var missing = range.Except(col);

And you could put the range-stuff into an Extension-Method

public static class extensions
{
    public static IEnumerable<DateTime> Range(this DateTime startDate, DateTime endDate)
    {
        return Enumerable.Range(0, (int)(endDate - startDate).TotalDays + 1)
                         .Select(i => startDate.AddDays(i));
    }
}

Then it would be simply

DateTime[] col = { new DateTime(2010, 1, 1),
                   new DateTime(2010, 1, 2),
                   new DateTime(2010, 1, 3),
                   new DateTime(2010, 1, 5)};

var start = new DateTime(2010, 1, 1);
var end = new DateTime(2010, 1, 6);
var missing = start.Range(end).Except(col);

But maybe this is not a high-performance-solution :-)

Depending on exactly what you are looking for and the sizes of the sets of data. A simple way would be to load the dates into a collection, then use a simple loop. I'll add a code sample here in a second.

DateTime currentDate = new DateTime(2010, 1, 1);
DateTime endDate = new DateTime(2010, 1, 6);
List<DateTime> existingDates = new List<DateTime>; //You fill with values
List<DateTime> missingDates = new List<DateTime>;

while(currentDate <= endDate)
{
    if(existingDates.contains(currentDate))
        missingDates.Add(currentDate);

    //Increment date
    currentDate = currentDate.AddDays(1);
}

Using this example you just need to load "existingDates" with the proper values, then the "missingDates" list will have your results

In .NET 2.0 :)

    static void Main(string[] args)
    {
        List<DateTime> dates = new List<DateTime>();
        dates.Add(new DateTime(2010, 01, 27));
        dates.Add(new DateTime(2010, 01, 30));
        dates.Add(new DateTime(2010, 01, 31));
        dates.Add(new DateTime(2010, 02, 01));


        DateTime startDate = new DateTime(2010, 01, 25);
        DateTime endDate = new DateTime(2010, 02, 02);

        List<DateTime> missingDates = new List<DateTime>(GetMissingDates(dates, startDate, endDate));

    }

    private static IEnumerable<DateTime> GetMissingDates(IList<DateTime> dates, DateTime startDate, DateTime endDate)
    {
        TimeSpan _timeStamp = endDate - startDate;
        DateTime _tempDateTime = startDate;
        IList<DateTime> _dateTimeRange = new List<DateTime>();
        IList<DateTime> _missingDates = new List<DateTime>();

        for (int i = 0; i <= _timeStamp.Days; i++)
        {
            _dateTimeRange.Add(_tempDateTime);
            _tempDateTime = _tempDateTime.AddDays(1);
        }

        foreach (DateTime dt in _dateTimeRange)
        {
            if (!dates.Contains(dt))
                yield return dt;
        }
    }

Lazy evaluated helper method aids in generating the list of dates to compare with. Might want to performance profile this method for large collections.

void Main()
{
    var dates = new[] {new DateTime(2000,1,1), new DateTime(2000,1,5)};
    DateHelper.Range(new DateTime(2000,1,1), new DateTime(2000,1,5)).Except(dates).Dump();
}

// Define other methods and classes here
public static class DateHelper {
    public static IEnumerable<DateTime> Range(DateTime start, DateTime end) {
        var days = end.Subtract(start).Days;
        var next = start;
        for(var i = 0; i<days; i++) {
            next = next.AddDays(1);
            yield return next;
        }
    }
}

var dates = new List<DateTime>
                {
                    new DateTime( 2010, 01, 01 ), 
                    new DateTime( 2010, 01, 02 ), 
                    new DateTime( 2010, 01, 03 ), 
                    new DateTime( 2010, 01, 05 )
                };

var targetDate = new DateTime( 2010, 01, 01 );

var missingDates = new List<DateTime>();
while ( targetDate <= new DateTime( 2010, 01, 06 ) )
{
    if ( !dates.Contains( targetDate ) )
        missingDates.Add( targetDate );

    targetDate = targetDate.AddDays( 1 );
}

foreach ( var date in missingDates )
    Debug.WriteLine( date.ToString() );

If you were thinking of solving this is LINQ, I do not believe it is possible unless you also had a list of all dates between the min and max date. In SQL, this amounts to a calendar table that contains all dates across a given time period.

Here is a LINQ solution where I create the Calendar list I mentioned above and then query for missing dates:

var dates = new List<DateTime>
                {
                    new DateTime( 2010, 01, 01 ), 
                    new DateTime( 2010, 01, 02 ), 
                    new DateTime( 2010, 01, 03 ), 
                    new DateTime( 2010, 01, 05 )
                };
var calendar = new List<DateTime>();
var targetDate = new DateTime( 2010, 01, 01 );
while ( targetDate <= new DateTime( 2010, 01, 06 ) )
{
    calendar.Add( targetDate );
    targetDate = targetDate.AddDays( 1 );
}

var missingDates = ( from date in calendar
              where !dates.Contains( date )
              select date ).ToList();

foreach ( var date in missingDates )
    Debug.WriteLine( date.ToString() );