Quickduck

9 Responses to “Reader challenge!”

1. November 4th, 2008 at 12:37 am #Ben

   I’ll start with a simple implementation that assumes the week begins on a Sunday.

   
   /// 
   
   /// Verify two dates are within the same 7 day week where the week begins on a Sunday.
   /// 
   public static bool InSameWeekSimple(this DateTime d1, DateTime d2) {   
   
               if (d2 < d1) { Swap(ref d1, ref d2); } // ensure d1 is less than or equal to d2
               DateTime beginningOfWeekDate2 = d2.AddDays(-(int)d2.DayOfWeek);
               return d1 >= beginningOfWeekDate2 && d1 < = d2; // verify that d1 is greater than the date that begins d2s week and less than d2.
   }
   

   
    private static void Swap(ref T obj1, ref T obj2) {
               var temp = obj1;
               obj1 = obj2;
               obj2 = temp;
   }
   

   This can be extended to work with a week beginning on a different day to Sunday:

   
   public static class ExtensionMethods {
   
     /// 
   
     /// Verify two dates are within the same 7 day week where the week begins on a Sunday.
     /// 
     public static bool InSameWeek(this DateTime d1, DateTime d2) {
       return InSameWeek(d1, d2, DayOfWeek.Sunday);
     }
   
     /// 
   
     /// Verify two dates are within the same 7 day week, specifying which   day begins the week.
     /// 
     public static bool InSameWeek(this DateTime d1, DateTime d2, DayOfWeek weekBeginDay) {
       if (d2 < d1) { Swap(ref d1, ref d2); } // ensure d1 is less than or equal to d2
       DateTime beginningOfWeekDate2 = d2.AddDays(-(int)d2.DayOfWeek);
       //DateTime beginningOfWeekDate2 = d2.AddDays(((weekBeginDay - d2.DayOfWeek) - 7)%7);
       return d1 >= beginningOfWeekDate2 && d1 < = d2; // verify that d1 is greater than the date that begins d2s week and less than d2.
     }
   
     /// 
   
     /// Verify two dates are within monday-friday of the same week.
     ///
     public static bool InSameWeekdays(this DateTime d1, DateTime d2) {
       if (IsWeekendDay(d1) || IsWeekendDay(d2)) { return false; }
       if (d2 < d1) { Swap(ref d1, ref d2); } // ensure d1 is less than or equal to d2
       return d1 >= d2.AddDays(-((int)d2.DayOfWeek - (int)DayOfWeek.Monday)) && d1 < = d2; // verify that d1 is greater than the date that begins d2s week and less than d2.
     }
   
     /// 
   
     /// Does the date provided fall on a Saturday or Sunday
     ///
     public static bool IsWeekendDay(DateTime date) {
       return date.DayOfWeek == DayOfWeek.Saturday || date.DayOfWeek == DayOfWeek.Sunday;
     }
   
     private static void Swap(ref T obj1, ref T obj2) {
       var tempDate = obj1;
       obj1 = obj2;
       obj2 = tempDate;
     }
   }
   
   

   All of these functions were unit tested and can be verified.

   Do I win?

2. November 4th, 2008 at 1:46 am #Drew Freyling

   Try the DateJs library. Its a great library with a heap of tools for all your dating needs.

3. November 4th, 2008 at 9:37 am #Andrew

   
public static bool InSameWeek(DateTime d1, DateTime d2)
{
Calendar cal = new GregorianCalendar();
int weekNo1 = cal.GetWeekOfYear(d1, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
int weekNo2 = cal.GetWeekOfYear(d2, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
return weekNo1 == weekNo2;
}


4. November 4th, 2008 at 9:48 am #gerrod

   Thanks for the answers guys.

   Ben’s answer was by far the most comprehensive and I’d lean towards that if I was making a DateTime library (which as Drew suggested, probably already exists).

   Andrew’s answer however is much simpler and closer to what I need for this particular purpose.

   Here’s what I came up with – essentially a cut down version of Ben’s. Note that itemDate is the date being tested:

   
   DateTime today = DateTime.Today;
   
   DateTime thisWeekStart = today.AddDays(
       DayOfWeek.Sunday - today.DayOfWeek);
   
   DateTime thisWeekEnd = today.AddDays(
       DayOfWeek.Saturday - today.DayOfWeek);
   
   if (itemDate > thisWeekStart && itemDate.Date <= thisWeekEnd)
       return "This week";
   

5. November 4th, 2008 at 12:26 pm #Andrew

   Yeah! Slow and simple wins the race. No wait, slow and special…. no wait…..

6. November 4th, 2008 at 10:42 pm #Ben

   We should do more of these challenges as I find I always learn something new.

   Thanks Andrew for pointing me towards the GregorianCalendar class.

7. March 18th, 2009 at 2:29 pm #Paulo Santos

   I think Andrew is far from being correct. Dates in different years will result in same week.
   And what happens on cases where the 1st of january is a wednesday and you compare 30/Dec with 2/Jan?

   I have now the same problem, I think I ll take a look at Ben’s solution.

8. March 18th, 2009 at 2:32 pm #Paulo Santos

   This should work

   public static bool InSameWeek(DateTime d1, DateTime d2)
   {
   DateTime beginningOfWeekDate1 = d2.AddDays(-(int)d2.DayOfWeek);
   DateTime beginningOfWeekDate2 = d2.AddDays(-(int)d2.DayOfWeek);
   return beginningOfWeekDate1 == beginningOfWeekDate2;
   }

   Thanks Ben!

9. March 18th, 2009 at 2:33 pm #Paulo Santos

   ops, there’s copy paste bug there.

   DateTime beginningOfWeekDate1 = d1.AddDays(-(int)d1.DayOfWeek);