周数和年份组合

Question

Several questions have been asked in the past on Weeknumber and Year in Excel, however, I have a specific question that I couldn't find the answer to.

I'm trying to get a combination of year and week number in the format of YYWW, so for example 1752, or 1801, based on a column with dates, something like this:

Date         Year  Week
01-01-2018   18    01
02-01-2018   18    01
...
31-12-2018   18    01

Year is simply determined by using the YEAR function on the date, and the week number is determined using the ISOWEEKNUM function on the date. This is then followed by some further processing, summing data based on year and week number, and the issue is that then also the data of the 31st of December 2018 is taken into account for week 1 of 2018, while the 31st of December is obviously not in week 1 of 2018, but in week 1 of 2019.

So the question is, how could I "fix" this, so how can I get Excel to give me 19 & 01 for 31-12-2018? Ideally I am looking for a solution that does not involve any VBA.

Any help is much appreciated!

Answer 1

For ISO week numbers the Thursday of each week will always be within the “isoweekyear”, so for any date, to get the correct year it's sufficient to find the year of that week's Thursday. You can do that like this:

=YEAR(A1+3-WEEKDAY(A1;3))

Answer 2

So in the end, thanks to the feedback of Nick and ImaginaryHuman072889, I fixed it like this:

=YEAR(A1)+IF(AND(MONTH(A1)=12;ISOWEEKNUM(A1)=1);1;0)+IF(AND(MONTH(A1)=1;ISOWEEKNUM>=52);-1;0)

I preferred not to nest the IF statements for readability and because they will never result in a TRUE at the same time anyway.

Answer 3

Just a couple of other options that worked for me:

=YEAR(A1)+AND(MONTH(A1)=12;ISOWEEKNUM(A1)=1)-AND(MONTH(A1)=1;ISOWEEKNUM>=52)

=YEAR(A1)+SWITCH(MONTH(A1)&ISOWEEKNUM(A1);"121";1;"152";-1;"153";-1;0)