In addition to the usual functions for data aggregation DAX has a special class of functions that change context of the execution for computing operations, and yet we call them the “iterators”. Sometimes we also call them the “X” functions, because after the name of the aggregation operation (SUM, AVERAGE, COUNT) stands the letter “X”, which indicates that these are iterators (SUMX, AVERAGEX, COUNTX). More in the text that follows…