Forum Discussion
Please explain cumulative sum work principle
Hi Anonymous,
There are two important points about this expression:
The use of ALL(Date) in order to ignore the current context. In fact, FILTER iterates over the entire table, analyzing dates that are outside of the current filter context. In this way, it will return date that are lower than or equal to the current filter.
The comparisons of Date[DateKey] against MAX(Date[Datekey]). When you are not familiar with DAX, these expressions look strange. However, if you recall the exact meaning of MAX , you see that it means "the maximum value of DateKey in the current context." Because the expression is part of CALCULATE filters, it still works in the original filter context. On the other hand, the expression Date[DateKey] is a column name, meaning "The value of DateKey in the current row context which is created by the FILTER during its iteration."
Hope it could help you better understand how it works. :smileyhappy:
Regards
Microsoft EmployeeHi Anonymous,
There are two important points about this expression:
The use of ALL(Date) in order to ignore the current context. In fact, FILTER iterates over the entire table, analyzing dates that are outside of the current filter context. In this way, it will return date that are lower than or equal to the current filter.
The comparisons of Date[DateKey] against MAX(Date[Datekey]). When you are not familiar with DAX, these expressions look strange. However, if you recall the exact meaning of MAX , you see that it means "the maximum value of DateKey in the current context." Because the expression is part of CALCULATE filters, it still works in the original filter context. On the other hand, the expression Date[DateKey] is a column name, meaning "The value of DateKey in the current row context which is created by the FILTER during its iteration."
Hope it could help you better understand how it works. :smileyhappy:
Regards
Ffitzpatrick47Helper II
I am going through this same issue on understanding, and the root of the confusion is the fact that semantically, Date[Datekey] means different things in this equation based on where it is in the equation. By itself, it means the row context, but within a filter that is within a calculate it means the filter context of the calculate. This isn't the only language where a variable means something different based on its location. Javascript's scope chain is also lexically scoped, but the rule there is really easy, you go up the scope chain, and if you can't figure out what the scope chain is, look in the debugger. Here, if it's in a "max" function it's in the filter context of the calculate, but what happens when you nest calculate functions. Further, what other functions have their own filter contexts? Sumx, sum?
I have to admit, among obiee, cognos, crystal and tableau, Dax is the hardest most inconsistent language I have ever tried to pick up. The others can be picked up in a few days, but not dax. I don't know who the target user is of the dax language, but it's not normal people. You can't just be a person of average programming ability and figure it out. Reducing 3sat to vertex cover, I figured out in 40 minutes. This calculate function is way harder for me. Congrats to all of you who have conquered it.
Hello, thanks for your explanation. But I still don't understant why the Date[Datekey] in Max() is under the current context. Why does the first parameter of Filter() not work on it?
