Dax - how to subtract one pivoted matrix column from another (power bi)

Question

With the columns of a denormalized source table pivoted to value rows in a matrix, what DAX would calculate the difference between matrix columns?

Selecting columns in Dax are one thing, but when columns are on rows, then how to select them?

There are many examples with date differences or adjacent rows, but those don't work here.

Answer 1

You can modify your filter context with CALCULATE similar to this:

Difference1 =
CALCULATE(SUM(Table1[value1]), Table1[class] = "C") - 
CALCULATE(SUM(Table1[value1]), Table1[class] = "A")