{:a "a"
 :b [{:a "a2" :c "c2"} {:a "a3" :c "c3"]
 :c "ignore"}

[["a" "a2" "c2"]
 ["a" "a3" "a3"]]

(let [{:keys [a b]} the-data]
  (for [{a2 :a, c2 :c} b]
    [a a2 c2]))