I like Koshke's answer, but if your rules for setting to NA don't have a nice mathematical property to them or you need to define your rules arbitrarily, this approach should give you that flexibility. First, define a function that returns the columns to drop based on your rules.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.