Domino Code Fragment

Code Name*
Calculate the week number in a year of a given date.		Date*
10/28/2025		Source (or email address if you prefer)*
[email protected]
IP address:.172.70.126.60
Description*
Calculates the week number in a year of a given date.		Type*
Formula		Categories*
Date/Time Handling
Implementation:
Required Client:
Server:
Limitations:
Comments:
Files/Graphics attachments (if applicable): Code:
This formula satisfies ISO 8601:1988:

REM "Replace D with the date of interest.";
D := [12/31/95];
FirstOfYear := @Date(@Year(D); 1; 1);
LastOfYear := @Date(@Year(D); 12; 31);
FirstDayNum := @Weekday(FirstOfYear);
LastDayNum := @Weekday(LastOfYear);
REM "ISO weeks start on Monday and ends on Sunday.";
ISOFirstDayNum := @If(FirstDayNum = 1; 7; FirstDayNum - 1);
ISOLastDayNum := @If(LastDayNum = 1; 7; LastDayNum - 1);
REM "The first and last ISO week is the first";
REM "and last ISO week to include Thursday";
IsFirstWeek := 7 - ISOFirstDayNum > 2;
IsLastWeek := 7 - ISOLastDayNum < 4;
REM "The date of the first day of the first ISO week";
ISOFirstDay := @If(IsFirstWeek;
           @Adjust(FirstOfYear; 0; 0; 1 - ISOFirstDayNum; 0; 0; 0);
           @Adjust(FirstOfYear; 0; 0; 8 - ISOFirstDayNum; 0; 0; 0));
REM "The date of the last day of the last ISO week";
ISOLastDay := @If(IsLastWeek;
           @Adjust(LastOfYear; 0; 0; 7 - ISOLastDayNum; 0; 0; 0);
  @Adjust(LastOfYear; 0; 0; -ISOLastDayNum; 0; 0; 0));
REM "Date outside ISOFirstDay and ISOlastDay";
REM "are from the previous or next year";
REM "Return the ISO week number and exit";
FirstWeekNextYear := @If(@Day(D) > @Day(ISOLastDay)
                      & @Year(D) = @Year(ISOLastDay);
           @Return(@Text(@Year(D)+1)+"W01"); NULL);
REM "I suspect this is where Julian dates would be useful";
REM "A recursive call could be used in a real language";
LastYear := (D - @Adjust(FirstOfYear; -1; 0; 0; 0; 0; 0))/60/60/24/7;
LastWeekLastYear := @If(@Day(D) < @Day(ISOFirstDay);
           @Return(@Text(@Year(D) - 1)+"W"+@Text(LastYear)); NULL);
REM "If you get this far, the date falls into an ISO week this year";
REM "Convert the difference in seconds to weeks";
NumWeeks := (D - ISOFirstDay)/60/60/24/7;
REM "Fractions indicate that the date falls";
REM "in the middle of the ISO week";
WeekAdjust := 1 - (NumWeeks - @Integer(NumWeeks));
ISOWeekNum := NumWeeks + WeekAdjust;
REM "Conform to ISO 8601 format";
Pad:=@If(ISOWeekNum<10;"0";"");
@Text(@Year(D))+"W"+Pad+@Text(ISOWeekNum)

Here is another version that gives you a week number in another ISO format:

REM "Formulae Calculate the Week Number(01-53) for any Date. ";
REM "The output follows the ISO 8601:1988 standard: ex 1997-W31-4 for 1997.07.31 ";
REM "Formulae writer : Nikolai Aasen ([email protected]), UNI Storebrand, Norway";
REM "Formulae written : 1997.07.30";
REM "Formulae updated : 1997.08.04";
REM "Version  : 1.03";
REM "Tested on   :Lotus Notes 4.6PreRelease2";
REM "This formulae is available in the";
REM "Lotus Notes FAQ: http://www.keysolutions.com/NotesFAQ/";
REM "More Calendar information in http://www.pip.dknet.dk/~pip10160/calendar.html";
REM "ISO 8601:1988 summary at: http://quake.stanford.edu/~lyle/ISOdate/Date.html";
REM "--------------------------------------------------------------------------------------------------";            
REM "Replace D with the date of interest.";
D := [1997.31.07];

REM "**************************";
REM"Calculate some data for this Year";
REM "**************************";
FirstOfYear := @Date(@Year(D); 1; 1);
LastOfYear := @Date(@Year(D); 12; 31);
FirstDayNum := @Weekday(FirstOfYear);
REM "ISO weeks start on Monday and ends on Sunday.";
ISOFirstDayNum := @If(FirstDayNum = 1; 7; FirstDayNum - 1);

REM " Week 1 of any year is the week that contains the first Thursday in January.";
REM "=1 if 1. jan = man - thu. WeekNumber is then 1, else 0";
IsFirstWeek := 7- ISOFirstDayNum >2;

REM "The first Monday after 1. jan this Year";
FirstMonday := 9 - ISOFirstDayNum;

REM "Number of Days from 1. jan to D";
DaysToDateD:=(D-FirstOfYear)/60/60/24+1;

REM "Number of days in Year(either 365 or 366)";
DaysInYear:=(LastOfYear-FirstOfYear)/60/60/24;

REM "Number of Weeks in Year. Most years have 52 weeks, but years that start on a
Thursday and leapyears that start on a Wednesday have 53 weeks.";
NumberOfWeeksThisYear:=@If( (ISOFirstDayNum=4 | (ISOFirstDayNum=3 &
DaysInYear=366));53;52 );

REM "***************************";
REM"Calculate some data for last Year  ";
REM "***************************";
FirstOfLastYear := @Date(@Year(D)-1; 1; 1);
LastOfLastYear := @Date(@Year(D)-1; 12; 31);
FirstDayNumLast := @Weekday(FirstOfLastYear);
REM "ISO weeks start on Monday and ends on Sunday.";
ISOFirstDayNumLast := @If(FirstDayNumLast = 1; 7; FirstDayNumLast - 1);

REM "Number of days in Year(either 365 or 366)";
DaysInYearLast:=(LastOfLastYear-FirstOfLastYear)/60/60/24;

REM "Number of Weeks Last Year. Most years have 52 weeks, but years that start on a
Thursday and leapyears that start on a Wednesday have 53 weeks.";
NumberOfWeeksLastYear:=@If( (ISOFirstDayNumLast=4 | (ISOFirstDayNumLast =3 &
DaysInYearLast=366));53;52 );

REM "************************";
REM"Calculates the Week Number  ";
REM "************************";


DDayNum := @Weekday(D);
ISODDayNum := @If(DDayNum = 1; 7; DDayNum - 1);

REM"Is D in the last Week of the last Year?";
DayInLastWeek := @If((DaysToDateD<FirstMonday & IsFirstWeek = 0);
                               @Return( @Text(@Year(D)-1)+"-W"+@Text(NumberOfWeeksLastYear)+"-"+@Text(ISODDayNum));
                                NULL);

REM "Calculate number of Complete Weeks Between D and 1.jan";
ComplNumWeeks:=@Integer((DaysToDateD-FirstMonday)/7);

REM "Are there remaining days?";
RemainingDays:=@If( (DaysToDateD+1-(FirstMonday+7*ComplNumWeeks))>0);

NumWeeks:= IsFirstWeek+ComplNumWeeks+1;

Out :=
@If(RemainingDays;
@If( (NumWeeks>52 & NumWeeks>NumberOfWeeksThisYear );
        @Return(@Text(@Year(D)+1)+"-W01-"+ @Text(ISODDayNum));
         @Return(@Text(@Year(D))+"-W"+@Right("0"+@Text(NumWeeks);2)+"-"+@Text(ISODDayNum)));
@Return(@Text(@Year(D))+"-W"+@Right("0"+@Text(NumWeeks-1);2) +"-"+@Text(ISODDayNum)));
Out