Here are some experiments that aren't polymorphic. The System/arraycopy
version is fastest, by far. Is there any good way to make the other
versions faster, or make them handle any array type?
(defn bconcat [& arrays]
(let [sizes (map count arrays)
sizes_r (vec (reductions + sizes))
offsets (cons 0 (drop-last sizes_r))
total (last sizes_r)
out (float-array total)]
(dorun (map #(System/arraycopy %2 0 out %1 %3) offsets arrays sizes))
out))
(defn cconcat [& arrays]
(let [vs (map vec arrays)
cc (apply concat vs)]
(float-array cc)))
(defn dconcat [& arrays]
(let [vs (map vec arrays)
cc (reduce into [] vs)]
(float-array cc)))
(defn econcat [& arrays]
(let [cc (reduce into [] arrays)]
(float-array cc)))
On Saturday, July 20, 2013 2:24:14 PM UTC-7, Brian Craft wrote:
>
> Is there an easy, fast way to concat primitive arrays? I was hoping java
> arrays had some common interface for this, but I haven't found much of use.
> I mostly see code like this:
>
> byte[] c = new byte[a.length + b.length];
> System.arraycopy(a, 0, c, 0, a.length);
> System.arraycopy(b, 0, c, a.length, b.length);
>
> which only works for bytes (in this case).
>
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