take-randnth.clj

(defn take-randnth [num coll]
  (take num
        (rest
         (map first
              (iterate (fn [[ret items]]
                         (let [idx (rand-int (count items))]
                           [(items idx)
                            (subvec (assoc items idx (items 0))
                                    1)]))
                       [nil
                        (vec coll)])))))

(defn lazy-shuffle [coll]
  ((fn shuffle [^clojure.lang.ITransientVector coll]
     (lazy-seq
      (let [c (count coll)]
        (when-not (zero? c)
          (let [n (rand-int c)]
            (cons (get coll n)
                  (shuffle (.pop (assoc! coll n (get coll (dec c)))))))))))
   (transient (vec coll))))