Check if a datetime is in same week as other datetime

Question

Let's say I have a list of dates in a table. Now I want to find all rows, which is in the same week as the date provided as an argument.

Let's say I have a table with:

• 2014-09-11
• 2014-09-12
• 2014-09-15

And I give this function the argument 2014-09-09, it has to look from monday->sunday, and realize that 09-11 and 09-12 is part of the week, but not 09-15.

How on earth to solve this?

I have thought on making a check on year, month and weeknumber, but you cannot guarantee that month is the same...

So how do you solve a problem like this?

Answer 1

why not?

bool AreFallingInSameWeek(DateTime date1, DateTime date2)
{
    return date1.AddDays(-(int)date1.DayOfWeek) == date2.AddDays(-(int)date2.DayOfWeek);
}

if you want to use any day other than Sunday as start of the week

bool AreFallingInSameWeek(DateTime date1, DateTime date2, DayOfWeek weekStartsOn)
{
    return date1.AddDays(-GetOffsetedDayofWeek(date1.DayOfWeek, (int)weekStartsOn)) == date2.AddDays(-GetOffsetedDayofWeek(date2.DayOfWeek, (int)weekStartsOn));
}

int GetOffsetedDayofWeek(DayOfWeek dayOfWeek, int offsetBy)
{
    return (((int)dayOfWeek - offsetBy + 7) % 7)
}

Answer 2

DxCk's comment is valid. This solution will work even if the first or last week of the year cross two different years:

Check that the first day of the week for both dates fall on the same day. Here is the code:

    private bool DatesAreInTheSameWeek(DateTime date1, DateTime date2)
    {
        var cal = System.Globalization.DateTimeFormatInfo.CurrentInfo.Calendar;
        var d1 = date1.Date.AddDays(-1 * (int)cal.GetDayOfWeek(date1));
        var d2 = date2.Date.AddDays(-1 * (int)cal.GetDayOfWeek(date2));

        return d1 == d2;
    }