clojure_puzzle_316.clj

;Attempt at the puzzle of issue 316 of Eric Normand newsletter.
;https://purelyfunctional.tv/issues/purelyfunctional-tv-newsletter-316-avoid-licensing-and-support-issues-with-the-right-jdk-for-you/

;Drop every nth element from a sequence
;The problem is simple: write a function that takes a number n and a sequence.
;The function returns a new sequence with every nth element removed.

;(drop-every 3 [:a :b :c :d :e :f :g])
;=> (:a :b :d :e :g)

;TODO The :when test is ugly, got a better idea?
(defn drop-every
  [n seq]
  (let [seq-indexed (map-indexed #(vec [%1 %2]) seq)]
    (for [[index val] seq-indexed
          :when (or (< (inc index) n)
                    (not (= 0 (mod (inc index) n))))]
      val)))

Old version was using keep-indexed but I couldn't make it work with nil values.