Business Day Calculation in Power Query

Data Transformation: Adding Business Days Excluding Holidays in Power Query

Problem Analysis

Transforming date-related data to account for business days while excluding holidays is a common issue in data analysis. This task involves:

1. Adding a specified number of business days to a given date.
2. Ensuring that weekends and holidays are excluded from the calculation.

Solution Outline

To address this problem in Power Query, we will:

1. Create a list of dates accounting for business days.
2. Exclude weekends from this list.
3. Exclude specified holidays from the final date list.
4. Create a custom function in M language to add business days.

Steps and Explanation

1. Create a List of Dates

Generate a list of dates starting from the given date and extending for the required number of days.

let
    StartDate = #date(2023, 10, 9),
    NumberOfDays = 30,
    DateList = List.Dates(StartDate, NumberOfDays, #duration(1, 0, 0, 0))
in
    DateList

2. Exclude Weekends

Filter out weekends from the DateList.

let
    StartDate = #date(2023, 10, 9),
    NumberOfDays = 30,
    DateList = List.Dates(StartDate, NumberOfDays, #duration(1, 0, 0, 0)),
    BusinessDays = List.Select(DateList, each Date.DayOfWeek(_, Day.Monday) < 5)
in
    BusinessDays

3. Exclude Holidays

Assume we have a list of holidays. We will exclude these from our BusinessDays list.

let
    StartDate = #date(2023, 10, 9),
    NumberOfDays = 30,
    DateList = List.Dates(StartDate, NumberOfDays, #duration(1, 0, 0, 0)),
    BusinessDays = List.Select(DateList, each Date.DayOfWeek(_, Day.Monday) < 5),
    Holidays = {
        #date(2023, 10, 10), 
        #date(2023, 10, 20)
    },
    BusinessDaysExcludingHolidays = List.Difference(BusinessDays, Holidays)
in
    BusinessDaysExcludingHolidays

4. Custom Function to Add Business Days

Create a custom M function to add a specified number of business days to a start date, excluding weekends and holidays.

// Function Definition
let
    AddBusinessDays = (startDate as date, daysToAdd as number, holidays as list) as date =>
    let
        DateList = List.Dates(startDate, daysToAdd + 60, #duration(1, 0, 0, 0)), // Adding buffer
        BusinessDays = List.Select(DateList, each Date.DayOfWeek(_, Day.Monday) < 5),
        BusinessDaysExcludingHolidays = List.Difference(BusinessDays, holidays),
        ResultDate = List.FirstN(BusinessDaysExcludingHolidays, daysToAdd){daysToAdd - 1}
    in
        ResultDate
in
    AddBusinessDays

// Usage Example
let
    StartDate = #date(2023, 10, 9),
    DaysToAdd = 15,
    Holidays = {
        #date(2023, 10, 10), 
        #date(2023, 10, 20)
    },
    Result = AddBusinessDays(StartDate, DaysToAdd, Holidays)
in
    Result

Promoting Best Practices

1. Modular Functions: Break down complex operations into modular functions for better readability and maintenance.
2. Error Handling: Implement error handling to deal with unexpected values or situations.
3. Reusable Code: Create reusable functions to save time on recurring tasks.

Further Learning

For a deeper understanding of Data Transformation and more advanced techniques, consider the courses offered on the Enterprise DNA Platform.

By following this structured approach, you can effectively add business days to a date in Power Query, excluding weekends and holidays. This method ensures accuracy and efficiency in handling date-related transformations.