Code Breakdown

This code snippet is written in DAX (Data Analysis Expressions), a formula language used in Power BI for data modeling and reporting. It defines a measure called "Comparison Sales Amount" that calculates the sales amount for a specific comparison period.

Variables

The snippet uses two variables, ComparisonPeriod and Result.

ComparisonPeriod

This variable is calculated using the CALCULATETABLE function. It creates a table or list of dates under specific conditions. The VALUES function is used to get a list of unique dates from the 'Date'[Date] field. REMOVEFILTERS removes any filters applied to the 'Date' table. Lastly, USERELATIONSHIP sets a temporary active relationship between 'Date'[Date] and 'Comparison Date'[Comparison Date] for the duration of the CALCULATETABLE operation.

Result

This variable calculates the "Sales Amount" for the comparison period defined by the previous variable. This is done with the CALCULATE function, which changes the context in which data is evaluated. In this case, it calculates "Sales Amount" for the dates in ComparisonPeriod.

Return

The code concludes by returning the quantity stored in the variable Result.

Concepts

Context and Filters in DAX

In DAX, the context refers to the specific conditions under which calculations are done. For example, calculating total sales over a given period. Filters modify the context and limit the scope of the data being evaluated. REMOVEFILTERS is used to return the context to its original state.

Relationships in DAX

USERELATIONSHIP is a DAX function that activates a relationship for the duration of a specific calculation. In this case, between the 'Date' and 'Comparison Date' fields.

Example

Consider a case where you have sales data for two years (2020 and 2021) and a separate table that maps each date in 2021 to the corresponding date in 2020 for comparison. This DAX code will calculate the sales amount for the 2020 date that corresponds to each 2021 date.