Enhancement request: ISO week number

Question

M language includes a function that returns the week number from a date: Date.WeekOfYear
However, it is much less flexible than the Excel 2010 Worksheet function WEEKNUM, which accepts a "return type" parameter. It can be used to return a ISO 8601 compliant week number. Ex: WEEKNUM(date,21).
It would be interesting to align the M function Date.WeekOfYear to the Excel WEEKNUM.
For those confronted to the challenge of building with Power Query a time dimension that includes an ISO week number, the following M code implements the formula found
in this blog. If you already have a column "Date", you can use the following code to add ISO year and week number columns:
InsertISOYear = Table.AddColumn(previousstepname, "ISOYear", each Date.Year(Date.AddDays([Date],3-Date.DayOfWeek([Date],1))), type number),
InsertRefDate = Table.AddColumn(InsertISOYear , "RefDate", each #date([ISOYear],1,3)),
InsertISOWeek = Table.AddColumn(InsertRefDate , "ISOWeek", each Number.IntegerDivide(Duration.Days( [Date]-[RefDate])+Date.DayOfWeek([RefDate],0)+6,7), type number ),
InsertWeekInt = Table.AddColumn(InsertISOWeek , "WeekInt", each [ISOYear] * 100 + [ISOWeek], type number),
InsertCalendarWeek = Table.AddColumn(InsertWeekInt , "WeekInCalendar", each Number.ToText([ISOYear]) & Number.ToText([ISOWeek],"-W00")),
RemovedColumns = Table.RemoveColumns(InsertCalendarWeek ,{"RefDate"})

Answer 1

I ran into the same issue, but had problems copying your solution. However, I think there is a quite simple alternative by using the Date.AddDays function. So instead of using e.g. Table.WeekOfYear([Date]) use Table.WeekOfYear(Date.AddDays([Date],-1)).
That substracts one day from the date and gives the Monday-Sunday weeknumber.