Clojure: sequence back to vector

Question

How can I cast a sequence back to vector after a sequence producing operation (like sort)? Does using (vec..) on a sequence that was a vector is costly?

One (bad?)

Answer 1

Meikel Brandmeyer just posted a solution to this on the Clojure group.

(defn sorted-vec
  [coll]
  (let [arr (into-array coll)]
    (java.util.Arrays/sort arr)
    (vec arr)))

Clojure's sort returns a seq across a sorted array; this approach does much the same thing, but returns a vector, not a seq.

If you wish, you can even skip the conversion back into a Clojure persistent data structure:

(defn sorted-arr
  "Returns a *mutable* array!"
  [coll]
  (doto (into-array coll)]
    (java.util.Arrays/sort))

but the resulting Java array (which you can treat as a Clojure collection in most cases) will be mutable. That's fine if you're not handing it off to other code, but be careful.