Get first date of ISO year

[RoyG]

Hello,

Is there a Dax code to get the first date of any given ISO year?

When I want to calculate the first date of a calender year then I use something like: 

VAR FirstDate = date(year(SelectedDate),1,1)

In this particular case I am looking for the first date in an ISO year. For example ISO year 2023 started on January 2nd as January 1st 2023 belongs to the ISO year 2022.  Similarly, ISO year 2021 started on January 4th.

Curious to see if anyone has a creative idea how to get to this date in DAX.

[RoyG · Accepted solution]

In case anyone is interested, I figured out a solution:

VAR FirstDate = date(year(SelectedDate),1,1)

VAR FirstISODate = if(weekday(FirstDates,2)<=4,FirstDates - weekday(FirstDates,2) + 1,FirstDates - weekday(FirstDates,2)+ 8)

This is based on the ISO rule: if 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in W01 (weekday 1 to 4). Otherwise it's part of the previous year.

[Keird]

Hi Roy, it does not allow for the first isoday being in the previous calendar year. That will be a problem in a year.

It is because the First Date is looking at the current year of the row, you want it to look at the first of januari of the iso year; so FirstDate = date( YearISO, 1, 1 )

VAR YearISO =

            IF (

                AND ( WeekISO < 5, WeekUS2 > 50 ),

                YearDate + 1,

                IF ( AND ( WeekISO > 50, WeekUS2 < 5 ), YearDate - 1, YearDate )

            )