Iterator functions also called X functions in Power BI DAX
What are Iterator Functions in Power BI?
In DAX (Data Analysis Expressions), iterator functions evaluate an expression row by row over a table and then aggregate the results.
They are also called X-functions because most of them end with X (like SUMX, AVERAGEX, MINX, MAXX, RANKX etc.).
They differ from normal aggregators (SUM, AVERAGE, MIN, MAX) because instead of working on a column directly, they iterate through a table, evaluate an expression, and then return a single result.
able → The table over which iteration will happen
Expression → The calculation performed on each row
Examples of Iterator (X) Functions
1. SUM vs SUMX
SUM: Adds up values in a column directly
SUMX: Iterates row by row and evaluates an expression
2. AVERAGEX
3. MINX / MAXX
4. RANKX
Key Difference: Normal vs Iterator