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X Functions in DAX

Matt Allington explains what that “X” means in functions like MEDIANX and also builds out a problem to solve:

An X function is a class of functions in DAX that are also known as “iterators” (note, there are other iterating functions too, like FILTER, but I am only referring to the X functions here). It is a big topic on its own, and this article is not going to be the definitive guide to X functions. But I will give you a couple of insights.

I have learnt a lot about how to teach people DAX over the last 6 years, and my teaching methods have evolved over that time. I remember fondly speaking at the Microsoft Data Insights Summit with Will Thompson on the topic “DAX 50 – DAX for the rest of us“. Will said to me “don’t mention the word ‘iterator’ as it is too confusing.”. I didn’t agree with Will at the time, but his comment stuck with me. Over time I have changed the day way I teach DAX. These days I show people how to add a calculated column in a table (everyone can do that – its dead easy). Then I explain that an X function does exactly the same thing, it’s just that you can’t see the interim results materialised in front of their eyes.

Click through to see what Matt means and stay tuned for the next episode of the X Functions, where Matt reveals that there are aliens by use of bi-directional relationships.

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