https://docs.google.com/spreadsheets/d/1Z9Wn9Kpe7nAR4nwfpPSNtvIAOkTtTp7IxV7WHp9a84M/edit?usp=sharing
I have a spreadsheet for the year. Every day is represented as its date and as its day of the week (bleu rows in the above spreadsheet). There is a blank column at the beginning of every month (ie, the "Febuary" column (greyed out in the above spreadsheet) doesnt increment the day of the week or the date).
What I want to do is, I want to look at either the day of the week or the date and write in above Sundays the week number. So "Wk01, Wk02, Wk03" up to Wk52. An example is marked in red on the link above. These "Wk"s would have 6 blanks between them (or 7 if the week is across the greyed out month column).
>Solution :
Use weeknum(), like this:
=arrayformula( if( B11:11 = "Sun", "Wk" & weeknum(B12:12), iferror(1/0) ) )