Federal holiday calculations

[Devin Asay]

On Aug 10, 2008, at 2:36 PM, Shari wrote:

> I found a Date/Time stack at http://www.troz.net/Rev/libraries.php
> for determining what day Easter falls on.
>
> Does anyone know of a stack or library that calculates the day of the
> month for U.S. major holidays for any given year?
>
> Such as thanksgiving(2011) returns the date Thanksgiving falls on in  
> 2011

Hi, Shari.

I wrote a handler to do this, based on information I found at the U.S.  
Naval Observatory web site. The hard part is figuring out the actual  
date for holidays like Memorial Day, AKA "the last Monday in May." The  
calling handler supplies the input in integers, and the function  
returns the date that the holiday falls on as date items. Then in the  
calling handler, you do whatever you need to do with that information.  
I use it in a scheduling application, so some aspects of the code,  
such as actual days off in cases where holidays fall on weekends, are  
specific to my app. But you may find it helpful in adapting to your  
own situation. Beware line wraps!

   ## Here are the basic formulas for computing U.S. holidays:

   #   FIXED DATE HOLIDAYS
   ##    New Year's Holiday: January 1  if on Sunday > Monday Jan 2nd  
off
   ##                                   if on Monday > Monday Jan 1st  
off
   ##                                   if on Tuesday, Wed, Fri > 31st  
and 1st off
   ##                                   if on Thurs > 1st and 2nd off
   ##                                   if on Sat > Dec 31st off
   ##    Independence Day: July 4       if on Sat > Friday 3rd off
   ##                                   if on Sun > Mon 5th off
   ##    Christmas Day:                 if on Sunday > Monday 26th off
   ##                                   if on Monday > Monday 25th off
   ##                                   if on Tuesday, Wed, Fri > 24th  
and 25th off
   ##                                   if on Thurs > 25th and 26th off
   ##                                   if on Sat > 31st off

   #   HOLIDAYS DETERMINED BY DAY OF WEEK AND MONTH
   ##    M.L. King Birthday: 3rd Monday in January
   ##    Presidents' Day: 3rd Monday in February
   ##    Memorial Day: Last Monday in May
   ##    Labor Day: First Monday in September
   ##    Thanksgiving: Fourth Thursday and following Friday in November

# called by: generateHolidayEvents
#  This function takes four integers as parameters:
##   the year, month, day of week, and an integer representing the  
ordinal.
## For example, if I want to find out the date of the fourth Thursday  
of November, 2008,
##  I would call:
##    put getDateOfNthWeekday(2008,11,5,4) into tDate
##  The function would return
##    2008,11,26,23,0,0,4

   function getDateOfNthWeekday year,monthNum,dayOfWeek,nth
   -- find what day is 1st of month
   -- get difference between that day and next monday
   -- add that difference in seconds to first day
   -- add number of needed weeks in seconds to get to nth monday
   put line monthNum of the monthNames && 1 & ", " & year into  
firstDayOfMonth
   convert firstDayOfMonth to dateitems
   put item 7 of firstDayOfMonth into theDayNum
   convert firstDayOfMonth to seconds
   --add 60*60 to firstDayOfMonth -- compensate for a quirk in  
converting between dateitems and seconds
   put 60*60*24 into scndsInDay
   if theDayNum < dayOfWeek then
     put dayOfWeek - theDayNum into daysToAdd
     put firstDayOfMonth + (daysToAdd * scndsInDay) into firstXday --  
X refers to the weekday we're interested in
   else if theDayNum > dayOfWeek then
     put 7 -(theDayNum - dayOfWeek) into daysToAdd
     put firstDayOfMonth + (daysToAdd * scndsInDay) into firstXday
   else
     put firstDayOfMonth into firstXday
   end if
   put firstXday + ((nth - 1) * 7 * scndsInDay) into nthXDay
   convert nthXDay to dateItems
   return nthXDay
end getDateOfNthWeekday


HTH

Devin

Devin Asay
Humanities Technology and Research Support Center
Brigham Young University