Shadow Filters.md

Shadow Filters Context

A shadow filter context is special kind of filter context, created by Iterators

When an iterator creates a row context, it also creates a shadow filter context.

Shadow filter context contains all the rows which are visible in the table that is iterated.

AVERAGEX (
    Customer, 
    CALCULATE ( SUM ( Sales[Quantity] ) )    
)    

Here AVERAGEX creates a shadow filter on the entire Customer table.

Shadow filter does not do anything.

The only function that can enable shadow filter is ALLSELECTED

When ALLSELECTED is called from inside an iteration, it restores the shadow filter.