Chris Webb and Matt Mason have both blogged about formulas for generating a date table using PowerQuery, but both of these posts focus on the standard year-month-day calendar. I’ve been doing a little work with some week based calculations and thought I would see how hard it would be to extend this sort of approach to generate some columns for a week hierarchy.

The ISO Week standard is part of ISO 8601 and defines a week as starting on Monday and ending on Sunday. That in itself is not very hard. The tricky bit comes into play when you go to assign each week to a year. Because weeks don’t fit evenly into years you need to either move some days from the end of December forward or move a few days of January back to the prior year.

The way to do this is as follows:

- Find the week that contains January 4 as that is always the first week of the year.
- If Jan 4 is before Thursday then any January days prior to Monday are allocated to the previous year.
- If Jan 4 is after Thursday then any December days at the start of the week are treated as being part of the current year.

I’ve also taken this a step further and created a small inline function that figures out the current 4-4-5 period and quarter that a given week falls into. I’m using a function which returns a record to return both the period and quarter from the one function which I think is pretty cool.

The following is an extension of Matt Mason’s method, he has some great screen shots of how to use the function so if you have not seen that post it’s definitely worth checking out.

Basically you start a new blank query, switch to the advanced mode and then paste in the following and invoke it:

let CreateDateTable = (StartDate as date, EndDate as date, optional Culture as nullable text) as table =>

let

DayCount = Duration.Days(Duration.From(EndDate – StartDate)),

Source = List.Dates(StartDate,DayCount,#duration(1,0,0,0)),

TableFromList = Table.FromList(Source, Splitter.SplitByNothing()),

ChangedType = Table.TransformColumnTypes(TableFromList,{{“Column1”, type date}}),

RenamedColumns = Table.RenameColumns(ChangedType,{{“Column1”, “Date”}}),

InsertYear = Table.AddColumn(RenamedColumns, “Year”, each Date.Year([Date])),

InsertQuarter = Table.AddColumn(InsertYear, “QuarterOfYear”, each Date.QuarterOfYear([Date])),

InsertMonth = Table.AddColumn(InsertQuarter, “MonthOfYear”, each Date.Month([Date])),

InsertDay = Table.AddColumn(InsertMonth, “DayOfMonth”, each Date.Day([Date])),

InsertDayInt = Table.AddColumn(InsertDay, “DateInt”, each [Year] * 10000 + [MonthOfYear] * 100 + [DayOfMonth]),

InsertMonthName = Table.AddColumn(InsertDayInt, “MonthName”, each Date.ToText([Date], “MMMM”, Culture), type text),

InsertCalendarMonth = Table.AddColumn(InsertMonthName, “MonthInCalendar”, each (try(Text.Range([MonthName],0,3)) otherwise [MonthName]) & ” ” & Number.ToText([Year])),

InsertCalendarQtr = Table.AddColumn(InsertCalendarMonth, “QuarterInCalendar”, each “Q” & Number.ToText([QuarterOfYear]) & ” ” & Number.ToText([Year])),

InsertDayWeek = Table.AddColumn(InsertCalendarQtr, “DayInWeek”, each Date.DayOfWeek([Date],1)+1),

InsertDayName = Table.AddColumn(InsertDayWeek, “DayOfWeekName”, each Date.ToText([Date], “dddd”, Culture), type text),

InsertWeekEnding = Table.AddColumn(InsertDayName, “WeekEndingFriday”, each Date.EndOfWeek([Date],6), type date),

InsertCurrentThursday = Table.AddColumn(InsertWeekEnding, “CurrentThursday”, each Date.AddDays([Date], -Date.DayOfWeek([Date],1) + 3), type date),

InsertISOWeekJan4 = Table.AddColumn(InsertCurrentThursday, “ISOWeekJan4”, each Date.FromText(Number.ToText(Date.Year([CurrentThursday])) & “-01-04”) ,type date),

InsertISOWeekYear = Table.AddColumn(InsertISOWeekJan4, “ISOWeekYear”, each Date.Year([CurrentThursday])) ,

InsertISOWeekFirstMon = Table.AddColumn(InsertISOWeekYear, “ISOWeekFirstMon”, each

if [CurrentThursday] < [ISOWeekJan4]

then Date.AddDays([CurrentThursday],-3)

else Date.AddDays([ISOWeekJan4], – Date.DayOfWeek([ISOWeekJan4],1) )

,type date),

InsertISOWeekNum = Table.AddColumn(InsertISOWeekFirstMon, “ISOWeekNum”, each Number.RoundUp(((Duration.Days(Duration.From([Date] – [ISOWeekFirstMon]))+1) /7 )), type number),

InsertISOWeekID = Table.AddColumn(InsertISOWeekNum, “ISOWeekID”, each [ISOWeekYear] * 100 + [ISOWeekNum], type number),

InsertISOWeekName = Table.AddColumn(InsertISOWeekID, “ISOWeekName”, each Text.From([ISOWeekYear]) & “W” & Text.End( “0” & Text.From(([ISOWeekNum]*10) + [DayInWeek]),3)),

InsertISOWeekNameLong = Table.AddColumn(InsertISOWeekName, “ISOWeekNameLong”, each Text.From([ISOWeekYear]) & “-W” & Text.End( “0” & Text.From([ISOWeekNum]),2) & “-” & Text.From([DayInWeek])),

fnPeriod445a = (weekNum) => let

Periods =

{

{(x)=>x<5, [P=1,Q=1]},

{(x)=>x<9, [P=2,Q=1]},

{(x)=>x<14, [P=3,Q=1]},

{(x)=>x<18, [P=4,Q=2]},

{(x)=>x<22, [P=5,Q=2]},

{(x)=>x<27, [P=6,Q=2]},

{(x)=>x<31, [P=7,Q=3]},

{(x)=>x<35, [P=8,Q=3]},

{(x)=>x<40, [P=9,Q=3]},

{(x)=>x<44, [P=10,Q=4]},

{(x)=>x<48, [P=11,Q=4]},

{(x)=>true, [P=12,Q=4]}

},

Result = List.First(List.Select(Periods, each _{0}(weekNum))){1}

in

Result,

InsertPeriod445 = Table.AddColumn(InsertISOWeekNameLong, “Period445Record”, each fnPeriod445a([ISOWeekNum])),

ExpandPeriod445 = Table.ExpandRecordColumn(InsertPeriod445, “Period445Record”, {“P”,”Q” }, {“Period445”, “Quarter445”}),

RemovedColumns = Table.RemoveColumns(ExpandPeriod445,{“CurrentThursday”, “ISOWeekFirstMon”})

in

RemovedColumns

in

CreateDateTable