I think i'm misunderstanding, rank is explicit throughout this example but i'm not familiar with this syntax (ruby maybe?) but whatever the case i don't see the rank polymorphism.

If i'm reading the syntax correctly, this would translate in kdb/q to a raze (flatten) on the 3 dimensions (regions, offices, employees). Probably more likely to be expressed as a converge but in either case, the calculations here are not possible in a rank polymorphic way.