Forum Discussion
Community Championcalculate "around" a variable
A variable in DAX is actually a constant. Unlike variables in other programming languages, once you declare a variable in DAX by assigning it a value, that value is immutable. Your variable __TodayVal in the CALCULATE for __PrevVal will not be affected at all by the filter argument.
Community ChampionA variable in DAX is actually a constant. Unlike variables in other programming languages, once you declare a variable in DAX by assigning it a value, that value is immutable. Your variable __TodayVal in the CALCULATE for __PrevVal will not be affected at all by the filter argument.
Community Champion- dedelman_clng
Hi AlB - so what you are saying is that once __TodayVal is evaluated it is the value itself, not the code that populated it. And applying a different filter context to a constant does nothing.
Thanks!
David
- AlB
dedelman_clng wrote:Hi AlB - so what you are saying is that once __TodayVal is evaluated it is the value itself, not the code that populated it. And applying a different filter context to a constant does nothing.
Thanks!
David
Yep. Exactly
You would need a measure instead for what you were trying to do.
- AlB
MFelix
Good point. I guess it comes down to nomenclature, to what exactly your definition of a constant entails.
What I said, or meant to say, is that once the variable is assigned a value (at creation) its contents are immutable. I am referring here to each execution instance of a variable. An instance of that variable exists between the point where it is created/assigned a value (which happens simultaneously) and the point where it is "used up" through RETURN.When in a calculated column we have something like:
VAR CurrentID = 'Table'[ID] RETURN CALCULATE ( SUM ( 'Table'[Sales] ); FILTER ( 'Table'; 'Table'[ID] < CurrentID ) )
we'll have, for each row, a different instance of the variable CurrentID. I am limiting my definition of constant to what happens within a row, which is the effective existence of each instance of CurrentID. And I emphasized that aspect because it was the culprit
in the issue presented by dedelman_clng
You are extending the definition to encompass all execution instances. If you consider it so, it is true that each instance will (possibly) be created with a different value. But that value will be immutable during a particular instance's life.
