Row Context:
DAX
expression normally operates on columns like:
GrossProfit:=SUMX(Sales,
Sales[Amount]-Sales[TotalCost])
*All functions that end in X are
iterators.
In above
example, you get the value of
Sales[Amount] for currently
iterated row by SUMX()
NumofAllProducts
:= COUNTROWS(Values(Product[ProductName]))
In this example, Product[ProductName] does not retrieve
value of ProductName for a specific row; instead column reference is used to
get values.
The concept of current row in first example of DAX
Expression is known as Row Context. You have a
row context whenever you iterate a table. Every iterator introduces a
row context and iterators can be nested. For example:
AverageDiscountedSalesPerCustomer :=
AVERAGEX (
Customer,
SUMX (
RELATEDTABLE
( Sales ),
Sales[SalesAmount]
* Customer[DiscountPct]
)
)
Filter Context:
The filter context is the set of
filters applied to the data model before the evaluation of a DAX expression
starts. When you use a measure in a pivot table, for example, it produces
different results for each cell because the same expression is evaluated over a
different subset of the data. The Microsoft documentation describes as query
context those filters applied by the user interface of a pivot table and as
filter context, those other filters applied by DAX expressions that you can
write in a measure. In reality, these filters are almost identical in their
effects (the real differences are not important for this introductive article),
so we simply defines as filter context the set of filters applied to the
evaluation of a DAX expression, usually a measure, regardless of how they have
been generated.
A
filter context automatically propagates through relationships, according to the
cross filter direction of the relationship. You
can control the filter context and its propagation using DAX functions such as
CALCULATE, CALCULATETABLE, ALL, VALUES, FILTER, USERELATIONSHIP, and
CROSSFILTER.
