handler.clj

(ns nested-vector-ops)

(def nested-vector [[:salt 0 5 :deviation 5 10]
                    [:milk 5 4 :deviation 1 2]
                    [:cream 0 0 :deviation 0 0]])

(->>
  nested-vector
  (remove (fn [[_ _ _ _ a]] (= "N/A" a)))
  (sort-by (fn [[_ _ _ _ a]] a))
  (reverse)) 

Oh. Well, just change zero? to a predicate that tests for N/A, e.g. (= "N/A", and then move the argument in the sort-by function to the fifth position.