Converting a date to a week number and vice versa
SearchDomino.com member Klavs Thor Olesan explains how to convert a date to a week number and vice versa using Formula Language.
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This tip shows you how to convert a date to a week number and vice versa using Formula Language. It was written at R4, and I can no longer remember why it works -- but it does.
The International Organization for Standardization defines Week 1 in a given year as the first week (starting Monday) that contains at least 4 January-days. In other words, Week 1 is the first week that includes a Thursday.
Code: Date -> Week Number: "SomeDate" is a date-time field containing a date. Jan1st := @Date(@Year(SomeDate); 1; 1); REM {Jan 1st same same year (not necessarily part of week 1)}; Adjust := 3 - @Modulo((@Weekday(Jan1st) + 1); 7); REM {Number of days to Monday week 1}; MondayW1 := @Adjust(Jan1st; 0; 0; Adjust;0; 0; 0); REM {Date for Monday week 1}; WeekNumber := 1 + @Integer(((SomeDate - MondayW1)\86400)\7) Note that LotusScript can return a Week Number for a Date directly. Week Number -> Date "SomeYear" is a numerical field containing a year. "SomeWeek" is a numerical field containing a week number. "SomeWeekday" is a numerical field containing a weekday number (Monday=1, Sunday =7) Jan1st := @Date(SomeYear; 1; 1); REM {Jan 1st same year (not necessarily part of week 1)}; Adjust := SomeWeekday +2 - @Modulo((@Weekday(Jan1st) + 1); 7); REM {Number of days to "SomeWeekday" week 1}; SomeWeekdayW1 := @Adjust(Jan1st; 0; 0; Adjust;0; 0; 0); REM {Date for "SomeWeekday" week 1}; Date := @Adjust(SomeWeekdayW1; 0; 0; 7 * (SomeWeek - 1); 0; 0; 0)
Klavs Thor Olesen says in in his tip that LotusScript can return a Week Number for a Date directly.
I would like to know how, because I have not found any method that does this.
—Goran L.
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It is the Format function I referred to. Here is an example:
Sub Click(Source As Button) Msgbox Format(Today, "ww"), 0+64+0+0, "Week number of Today" End Sub
—Klavs Thor Olesen, tip author
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This is exactly what I was looking for. I was looking for a formula to calculate a week number field on a form based on a date entered in another field. I typed in calculate week number in a search engine and there it was, number eight in my search results. It's just what I was looking for and it does exactly what I need it to do. I set the properties of the new field to compute after validation and it works perfectly. Thanks very much.
—Bob V.
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Here is the same function converted to LotusScript:
--Code start-- Function fWeekNumberDate (numYear As Integer, numWeekNo As Integer, numWeekDay As Integer ) As Variant %REM Version 1.0 Author: Andrew Dempster, Constellation Europe Ltd Date: 28/06/2007 Cobbled together from various places this script is a duplicate of a @Formula that returns a date from a week number and day "numYear" is a numerical value containing a year. "numWeekNo" is a numerical value containing a week number. "numWeekDay" is a numerical value containing a weekday number (Sunday=1, Monday=2, Saturday =7) %END REM Dim numAdjust As Integer Dim dtJan1st As NotesDateTime Dim dtSomeWeekDayW1 As NotesDateTime Set dtJan1st = New NotesDateTime ("01/01/" & Cstr(numYear)) '/* Jan 1st same year (not necessarily part of week 1) numAdjust = numWeekDay + 1 - (Weekday(dtJan1st.DateOnly)+1) Mod 7 '/* Number of days to "numWeekDay" week 1 Call dtJan1st.AdjustDay(numAdjust, True) Set dtSomeWeekDayW1 = New NotesDateTime(dtJan1st.DateOnly) '/* Date for "numWeekDay" week 1 Call dtSomeWeekDayW1.AdjustDay (7 *(numWeekNo -1)) fWeekNumberDate = dtSomeWeekDayW1.DateOnly End Function --Code end--
Also, here's a handy hint for the Formula code, using correct weekdays:
--Code start-- N := "1" : "2" : "3" : "4" : "5" : "6" : "7"; Days := "Sunday" : "Monday" : "Tuesday" : "Wednesday" : "Thursday" : "Friday" : "Saturday"; SomeWeekday := @TextToNumber (@Replace(Day;Days;N)); <-- Where Day is your Text date field Adjust := SomeWeekday + 1 - @Modulo((@Weekday(Jan1st) + 1); 7); <- Changed to +1 as days now in line with @WeekDay function! --Code end--
I hope this helps (I've got a calendar population routine in the pipeline that I shall be submitting later). A huge thanks to Klavs for this function; it's a lifesaver!
—Andrew D.
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