Get Date of every alternate Friday

Question

I am wondering if i can get the date of every alternate friday starting with 13th of April, 2012 to give it as a parameter to a stored procedure using c#, asp.net?

It should also be most recently passed date. Thank you!

Well do you want it from 4/13/12 or from the most recent Friday? And to what date do you want it to end..? — Nick Rolando, Apr 17 '12 at 18:55
@Shredder It should give me most recent alternate friday which was started on 13th of April :-( Its weird but i cant say the end date! — challengeAccepted, Apr 17 '12 at 18:59
@Ram start from 4/13/12 to most recent alternated friday? see if my answer helps. good luck — Nick Rolando, Apr 17 '12 at 19:10

score 8 · Accepted Answer · answered Apr 17 '12 at 18:59

Just set a DateTime with the date you want to start at, and then keep adding 14 days:

So to get every other Friday after 4/13 until the end of the year:

DateTime dt = new DateTime(2012, 04, 13);
while (dt.Year == 2012)
{
    Console.WriteLine(dt.ToString());
    dt = dt.AddDays(14);
}

More info after comment:

If you want the most recent alternate Friday since 2012/04/13, you can compute the number of days between now and 2012/04/13, take the remainder of that divided by 14, and subtract that many days from today's date:

DateTime baseDate = new DateTime(2012, 04, 13);
DateTime today = DateTime.Today;

int days = (int)(today - baseDate).TotalDays;
int rem = days % 14;
DateTime mostRecentAlternateFriday = today.AddDays(-rem);

Your answer is terrific! Thank you! – challengeAccepted Apr 17 '12 at 19:17 — challengeAccepted, Apr 17 '12 at 19:17

score 2 · Answer 2 · answered Apr 17 '12 at 19:01

2

You can easily make a generator method that would give you the set of fridays:

public IEnumerable<DateTime> GetAlternatingFridaysStartingFrom(DateTime startDate)
{
    DateTime tempDate = new DateTime(startDate.year, startDate.Month, startDate.Day);

    if(tempDate.DayOfWeek != DayOfWeek.Friday)
    {
        // Math may be off, do some testing
        tempDate = tempDate.AddDays((7 - ((int)DayOfWeek.Friday - (int)tempDate.DayOfWeek) % 7);
    }

    while(true)
    {                
        yield return tempDate;
        tempDate = tempDate.AddDays(14);
    }
}

Then, simply use some LINQ to determine how much you want:

var numberOfFridays = GetAlternatingFridaysStartingFrom(DateTime.Today).Take(10);

answered Apr 17 '12 at 19:01

Tejs

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DateTime is a struct, and therefore values are copied. There is no need for a temp date; you can just use the parameter; If you want it in a new variable just for a different name, just assign startDate to TempDate and it will perform a deep copy. Also, more readable way to get to the next friday is `while(tempDate isn't friday)tempDate.AddDays(1)` It doesn't perform quite as well, but it's still constant time so who cares. – Servy Apr 17 '12 at 19:06
Potentially, but someone could pass a date time with minutes and seconds information, and I didnt want to copy that forward. This way, you just get a XX/YY/ZZ 00:00.000 datetime. – Tejs Apr 17 '12 at 19:08
You can use the `Date` property for that. `tempDate = startDate.Date` Then it makes the intention clearer in code. – Servy Apr 17 '12 at 19:10
Possible way to use this method: `var dates = GetAlternatingFridaysStartingFrom(startingDate).TakeWhile(date => date < endingDate);` – Servy Apr 17 '12 at 19:11

score 0 · Answer 3 · answered Apr 17 '12 at 19:01

Why do you need a stored proc?

If you have a date that is Friday, why not just use AddDays(14) in a loop?

If you want to find the nearest Friday from a start date, just use this:

while(date.DayOfWeek != DayOfWeek.Friday)
{
    date.AddDays(1);
}

Then use the 14 day loop to get every other Friday.

score 0 · Answer 4 · answered Apr 17 '12 at 19:13

You can create simple method that will enumerate them like so:

public static IEnumerable<DateTime> GetAlternatingWeekDay(DateTime startingDate)
{
    for (int i = 1; ; i++)
    {
        yield return startingDate.AddDays(14*i);
    }
}

Which you can call like this:

DateTime startingDate = DateTime.Parse("2012-04-13");
foreach (var date in GetAlternatingWeekDay(startingDate).Take(10))
{
    Console.WriteLine(date.ToString("R"));
}

Alternately, if you need to know the date for a given number of weeks out, you could use code like this:

DateTime date = DateTime.Parse("2012-04-13").AddDays(7 * numberOfWeeks);

Get Date of every alternate Friday

4 Answers4