如何从ISO日期和星期获取月份

Question

I'm looking for a way to convert an ISO date to Month and I also need to covert an ISO week to Month. I need to do this in Excel and Access. I found this formula for excel but when converting it to Access it does not work. Is there a simple way to accomplish this? I found this Excel formula to convert ISO date to month (C2=date) and it works perfect:

=MONTH(DATE(YEAR(C2),MONTH(C2)+(WEEKDAY(C2,2)+(DAY(DATE(YEAR(C2),MONTH(C2)+1,0)))-(DAY(C2))<4),(((7-(WEEKDAY(C2,2)))+(DAY(C2)))>3)))

But when I modify it for an Access query it does not return the correct values:

Date_to_Month:MONTH(DATESERIAL(YEAR([WW_Index].[ISO_date]),MONTH([WW_Index].[ISO_date])+(WEEKDAY([WW_Index].[ISO_date],2)+(DAY(DATESERIAL(YEAR([WW_Index].[ISO_date]),MONTH([WW_Index].[ISO_date])+1,0)))-(DAY([WW_Index].[ISO_date]))<4),(((7-(WEEKDAY([WW_Index].[ISO_date],2)))+(DAY([WW_Index].[ISO_date])))>3)))

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I also need to convert ISO week_year to Month. I found this formula but it does not work:

=MONTH(DATE(YEAR(C2),1,-2)-WEEKDAY(DATE(YEAR(C2),1,3))+D2*7)

Example: week 18, 2012 is the ISO week of Apr 30 through May 6, 2012. There is less that 4 April days in this week thus week 18, 2012 is in May.

Any help would be greatly appreciated.

Answer 1

I don't know access but you can do the first part (date to month) much more easily in excel with this formula

=MONTH(C2-WEEKDAY(C2-1)+4)

That should be easier to convert for access......

For the second part you are finding the Monday of the relevant week, hence you get the wrong month in some cases, the Thursday of the week (midpoint) should always be within the correct month so you can just add 3 to get that (-2 becomes 1), ie

=MONTH(DATE(YEAR(C2),1,1)-WEEKDAY(DATE(YEAR(C2),1,3))+D2*7)

I assume C2 is a date within the relevant year and D2 is the ISO week number but probably better to have C2 containing the year, eg just 2013 and then you can use

=MONTH(DATE(C2,1,1)-WEEKDAY(DATE(C2,1,3))+D2*7)