merge ordered seqs example

mergeseq.clj

;; austin clojure meetup hacking


;; ----------------------------------------
;; just merge 2 seqs

(defn merge2 [s1 s2]
  (if (seq s1)
    (when (seq s2)
      (let [i1 (first s1)
            i2 (first s2)]
        (if (< i1 i2)
          (cons i1 (lazy-seq (mergeseq (rest s1) s2)))
          (cons i2 (lazy-seq (mergeseq s1 (rest s2)))))))
    s2))

;; ----------------------------------------
;; merge N seqs

(defn index-of-min [colls]
  (loop [best nil
         best-index nil
         colls colls
         i 0]

    (if (seq colls)
      (if-let [n (first (first colls))]
        (if (or (nil? best) (< n best))
          (recur n    i          (rest colls) (inc i))
          (recur best best-index (rest colls) (inc i)))
	(recur best best-index (rest colls) (inc i)))
      best-index)))

(defn mergen [colls]
  (when-let [i (index-of-min colls)]
    (cons (first (nth colls i))
          (lazy-seq (mergen (update-in colls [i] rest))))))