How to calculate based on current selection ?

[Anonymous]

Here is expression : sum ( sales) 

Here is dimension : Yr = ( 2015, 2016, 2017)

How do I write expression so it returns values for ANY YEAR selected  minus prior year ?

[Anonymous · Accepted solution]

sum({<Yr= {'$(=max(Yr))'}>}sales) - sum({<Yr= {'$(=max(Yr)-1)'}>}sales)