Implementing iterators

In DAX, iterators are functions that evaluate an expression for every row of a table and then aggregate the result. These functions are called iterators because the functions iterate over each row of a table. Within DAX, iterator functions end with an X character and include the following functions:

• AVERAGEX
• COUNTAX
• COUNTX
• GEOMEANX
• MAXX
• MEDIANX
• MINX
• PRODUCTX
• STDEVX.P
• STDEVX.S
• SUMX
• VARX.P
• VARX.S

Each of these iterator functions performs exactly the same calculation as their non-X equivalent aggregation functions, except that the X functions perform their aggregation over a table specified as the first parameter of the function.

All of these iterator functions have the following general form:

<function>(<table>, <expression>)

Here, <function> is the name of the iterator function. Each iterator function takes a table as its first parameter as well as a DAX expression as its second parameter. The expression is evaluated for each row of the table and then the aggregation function aggregates the results of each of those evaluations.