Date.DatesBetween to retrieve dates between 2 dates in Power BI and Power Query

Today I’m sharing a handy function with you that allows you to retrieve all or just a couple of dates between 2 given dates: Date.DatesBetween.

Usage

This function takes 3 parameters:

  1. From- or Start-date
  2. To- or End-date
  3. A selection of ONE of these intervals: Year, Quarter, Month, Week or Day

All dates will be created at the end of the chosen interval: So if you want to analyse events with a duration for example, where you want to transform your data to show one day per (monthly) event, this function generates month-end-dates for every month within the timespan. Please not that if the To-/End-date is within a month, the last element of the list will NOT be that day, but the day of the end of that month.

The default-value for the 3rd parameter is “Day”, so if you omit the specification, the function will return a list of all days in between.

Definition

How it works

This function uses Function.Invoke to create a compact code. In step “CaseFunction” (rows 12-18), a table is created that contains all the elements for a case-selection. The first column contains the case that is selected by the 3rd parameter. The other columns contain the functions and expressions for the cases.

Table with all different elements for each case

Step “Case”  filters that table down to one remaining record:

Case = CaseFunctions{[Case = TimeInterval]},

It uses a special row-selector { [NameOfTheColumn = Condition] } that only works for columns containing unique keys.

Step “DateFunction” has the command that creates the list of dates:

DateFunction = List.Transform({0..Case[NumberOfAddedTIs]-1}, each Function.Invoke(Case[LastDateInTI], {Function.Invoke(Case[TypeOfAddedTI], {From, _})} ))

Starting with creating a list with the length of the number of intervals (yellow). The next evaluation step uses  Function.Invoke (green): This allows us to work with the function name as a variable from our Case-record. So whatever has been selected for “TypeOfAddedTI” (Time Interval) will be executed with From and the respective number from our list as its parameter (like: Date.AddWeeks(From, 2) for the third item of the list if “Week” is selected. The last evaluation-step (orange) will be Function.Invoke(CaseLastDateInTI) which shifts every returned date at the end of its Interval (here: Date.EndOfWeek).

Of course, this coding style is a matter of taste, but I found it worth sharing.

Enjoy & stay queryious 😉