Three ways of distinctifying a sequence and returning a vec

distinctify.clj

(defn unique-vec1
  "Straight-up Clojure sequence traversal"
  [s]
  (vec (set s)))

(defn unique-vec2
  "Conj into transient set and vectorize"
  [s]
  (loop [remaining s
         seen (transient #{})]
    (if (empty? remaining) (vec (persistent! seen))
      (recur (next remaining) (conj! seen (first remaining))))))

(defn unique-vec3
  "Use set as distinctifier, but conj into transient vector"
  [s]
  (loop [remaining s
         seen #{}
         out (transient [])]
    (if (empty? remaining) (persistent! out)
      (let [this (first remaining)]
        (if (contains? seen this) 
          (recur (next remaining) seen out)
          (recur (next remaining) (conj seen this) (conj! out this)))))))