Could you do a datediff function? dateadd('week',-datediff('week',datetrunc('year',[date]),[date])+1,[date])
So this equation would get the number of weeks between the first of the year and the target date, then subtract the number of weeks and add 1 to account for week 1 to the date to adjust it back to january and then anything else should reference whatever date you choose.
I tried this, but it is giving the result as 1/7/2018 and it's week. Maybe I missed something.
Could you please explain, how I can get 'Week 1' as text for week of 3/4/2018 and 'Week 2' as text for week of 3/11/2018 and so on.
It appears that this one is a unique case, the first sunday of the month is the 7th, so technically the way tableau would calculate it as the first full week would be week 53 of 2017 instead of week 1 of 2018. You could also do a calculated field like this
'Week ' + Str(DATEDIFF('week',[Date],[Date]+7))