First day of a week

[Cpirino]

Hi, I have a week number like a 35 and I need the first day of this week.

[TylerNa]

You'll need to have the year associated with the week number and then you can utilize one of these solutions.

[steven-barsalou]

There are some other good leads to a solution above.  It all depends on how you define the first week of the year, but you can calculate a formula to calculate the Monday of the week, order them, then add a record ID.  That will give you a week number.

To calculate the Monday of the week, you can use a formula like the one below.  This is SQL, but you should be able to easily convert it into an Alteryx formula.

Cast(calendar_date - ((calendar_date- Cast('1900-01-01' As Date)) Mod 7 ) As Date) As monday_of_week

[jwalder · Accepted solution]

Presumes current year by using DateTimeNow() but that could be replaced with an date in a column to get the year of it instead. [week] is then the numeric week number. Using these offsets, Sunday is first day.

DateTimeAdd(DateTimeAdd(DateTimeTrim(DateTimeNow(),'year'),[week]*7,'days'),switch(DateTimeFormat(DateTimeAdd(DateTimeTrim(DateTimeNow(),'year'),[week]*7,'days'),'%a'),0,'Mon',-1,'Tue',-2,'Wed',-3,'Thu',-4,'Fri',-5,'Sat',-6,'Sun',0),'days')

[AlRoBo]

I wanted to get the first day of the week using a single formula instead of a bunch of tools, so I converted this from steven-barsalou's SQL as recommended.

I wanted my week to begin with Sunday, so I changed '1900-01-01' to '1899-12-31'. Here is the Alteryx formula:

DateTimeAdd([DateTimeNow],Mod(
DateTimeDiff(ToDate('1899-12-31'),[DateTimeNow],'days')
,7),'days')