How to know whether there is any overlap in a collection of periods using LINQ

Question

I have a collection of periods [FromDate, ToDate].

I would know whether there is any overlap between a given period and the periods in the collection.

Answer 1

Approach it this way instead: There is no intersaction if the check date's todate < the from date, or the check date's fromdate > the to date. This is assuming check.from <= check.to.

Periods.Any(p => !(check.ToDate < p.FromDate || check.FromDate > p.ToDate));

or (after unwrapping the negative):

Periods.Any(p => check.ToDate >= p.FromDate && check.FromDate <= p.ToDate));

Answer 2

Do 2 periods having common date, say ToDate for period 1 and FromDate of period 2 are the same, count as in intersection ?

If yes then a little modification to your query to simply check the dates of a period if are within the checked period separately as if one of the dates falls inside a period then there is intersection:

bool conflict = Periods.Any(p => ((p.FromDate >= periodToCheck.fromDate && 
                                    p.ToDate <= periodToCheck.fromDate)
                                  ||
                                   (p.FromDate >= periodToCheck.toDate && 
                                    p.ToDate <= periodToCheck.toDate))
                             );

Answer 3

If FromDate <= ToDate always holds true for your Period objects, you can define a helper extension method OverlapsWith as follows:

public static bool OverlapsWith(this Period a, Period b)
{
    return !(b.ToDate <= a.FromDate || a.ToDate <= b.FromDate);
}

To illustrate what's going on, let's look at the two cases where there is no overlap between a and b:

//                         a
//                |-----------------|
//   |--------|                          |-----------|
//       b1                                    b2

You can check the above condition against this diagram. Since the diagram shows the cases where no overlap occurs, but the method really ought to test for overlap, the condition needs to be negated. It could be simplified to the following:

           b.ToDate > a.FromDate && a.ToDate > b.FromDate

When you use this method in a LINQ query, it turns out very easy to understand:

    Periods.Any(period => period.OverlapsWith(periodToCheck))

Answer 4

You may find the following article useful and especially the TimePeriodIntersector class.

Sample excerpt:

public void TimePeriodIntersectorSample()
{
    TimePeriodCollection periods = new TimePeriodCollection();

    periods.Add( new TimeRange( new DateTime( 2011, 3, 01 ), new DateTime( 2011, 3, 10 ) ) );
    periods.Add( new TimeRange( new DateTime( 2011, 3, 05 ), new DateTime( 2011, 3, 15 ) ) );
    periods.Add( new TimeRange( new DateTime( 2011, 3, 12 ), new DateTime( 2011, 3, 18 ) ) );

    periods.Add( new TimeRange( new DateTime( 2011, 3, 20 ), new DateTime( 2011, 3, 24 ) ) );
    periods.Add( new TimeRange( new DateTime( 2011, 3, 22 ), new DateTime( 2011, 3, 28 ) ) );
    periods.Add( new TimeRange( new DateTime( 2011, 3, 24 ), new DateTime( 2011, 3, 26 ) ) );

    TimePeriodIntersector<TimeRange> periodIntersector = 
                    new TimePeriodIntersector<TimeRange>();
    ITimePeriodCollection intersectedPeriods = periodIntersector.IntersectPeriods( periods );

    foreach ( ITimePeriod intersectedPeriod in intersectedPeriods )
    {
        Console.WriteLine( "Intersected Period: " + intersectedPeriod );
    }
    // > Intersected Period: 05.03.2011 - 10.03.2011 | 5.00:00
    // > Intersected Period: 12.03.2011 - 15.03.2011 | 3.00:00
    // > Intersected Period: 22.03.2011 - 26.03.2011 | 4.00:00
} // TimePeriodIntersectorSample