Is there a way to create an array with the type of another array? (type arr) returns the array type, but make-array wants the element type not the array type, so
(make-array (type arr) n) doesn't work as one might hope. On Sunday, July 21, 2013 8:36:22 AM UTC-7, Alex Fowler wrote: > > Java's System.arraycopy is the fastest you can get, since it delegates > execution to a function implemented in C inside JVM. Simply, this is the > fastest that your computer hardware can get. All in all Java arrays meet > the same difficulties and implications as C arrays and that is why > concationation of raw arrays is so "complex", in contrast to higher-level > collections which use objects and pointers (e.g. LinkedList). In other > words, difficulties you experience are natural outcome of how computer's > memory management is made and there is no way around them. You get the most > of the speed from arrays because they are solid (not fragmented) chunks of > bytes allocated in memory in the moment of their creation. For that very > reason you cannot extend an existing array (the size cannot be changed > after creation) and you can't concatenate it with another array since first > it would have to be concatenated. > > The natural outcome also is that only arrays of same types can be > concatenated with System.arraycopy since only array pointers store type > data, and the contents are simply untyped bytes. And this is why it is > byte-level and no type-checks are ever done besiedes the initial > type-check. Again, higher-level pointer-based data structures like > LinkedList or Queue can introduce boxed typed values, but that'd be waaay > slower. Considering that only arrays of same type are concatenateable, > creating a polymorphic function is easy - simply check the argument type > like: > > ; first save types to use them later > (def arr-type-int (class (ints 3))) > ; ... same for other primitives... > > ; then in your func: > (cond > (= (class arr) arr-type-int) (do-int-concat) > ...) > > For more reference: > http://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html > http://docstore.mik.ua/orelly/java-ent/jnut/ch02_09.htm > > As an alternative, try looking into Java NIO buffers - they too are fast > and too have some limits. But maybe you could make good of them, depends on > your use case. > > Although somewhat in another vein, but still relating fast data management > is https://groups.google.com/forum/?hl=en#!topic/clojure/BayfuaqMzvs which > brings in C-like structs in. > > On Sunday, July 21, 2013 2:39:38 AM UTC+4, Brian Craft wrote: >> >> 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). >>> >> -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
