For minimal change to the presented code, what about
(defprotocol appendable (append-to [this ^StringBuilder sb]))
(extend-protocol appendable
String
(append-to [this ^StringBuilder sb] (.append sb this))
clojure.lang.IFn
(append-to [this ^StringBuilder sb] (this sb))
Object
(append-to [this ^StringBuilder sb] (.append sb (str this))))
(defn final-str [a]
(let [sb (StringBuilder.)]
(append-to a sb)
(str sb)))
(defn par-join [sep xs]
(fn [sb]
(when-let [xs (seq xs)]
(append-to (first xs) sb)
(doseq [x (next xs)]
(append-to sep sb)
(append-to x sb)))))
(let [f #(->> % (map (comp val)) (par-join ","))]
(->> data-struct
(map f)
(par-join "\n")
final-str))
Which winds up taking about a second and only creates one StringBuilder.
On Fri Feb 13 2015 at 8:02:27 PM Andy Chambers <[email protected]>
wrote:
> Is there a reason you're collecting the result into a string rather than
> just writing out to a file?
>
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