Counting subscribers with matching ZIP code, interests, and sex
The first thing I notice is that you're calling map.{}.compact when you probably could be calling select{}, that is, you want to select from self.distribution. So that would replace 6 method calls with 3.

If you use select, it always returns an array and never a nil, so instead of unless X.nil or X.empty, you could use if X.any?, which would replace 6 method calls with three.

If you aren't using @matched_zips outside of this context, it makes no sense to assign a variable here. Instead of assigning, you could just use (CardSignup.all.map(&amp;:zip_code) &amp; @zip_codes).each do, which would spare you three variable assignments.