The original code looked like someone had learned old-school C++ and just shoehorned that into python. This phenomenon is all over physics. The fixed code isn't just short, it's idiomatic and clear (YMMV) and hence much easier to understand.

Reasonably modern C++ would allow you to define a Counter class, and to define maps and filters, if the stdlib versions don't work for you for whatever reason.

Fortran, on the other hand,...