Glad you've found it! :D As an off-topic side-note: please, use no underscores in naming, use hyphens instead, this is lisp's style... like "sizes_r" become "sizes-r". Many ppl will thank you later :)
On Sunday, July 21, 2013 11:39:17 PM UTC+4, Brian Craft wrote: > > Using getComponentType, it appears to be handling different primitive > array types ok: > > (defn fconcat [& arrays] > (let [sizes (map count arrays) > sizes_r (vec (reductions + sizes)) > offsets (cons 0 (drop-last sizes_r)) > total (last sizes_r) > out (make-array (.getComponentType (class (first arrays))) total)] > (dorun (map #(System/arraycopy %2 0 out %1 %3) offsets arrays sizes)) > out)) > > > > On Sunday, July 21, 2013 12:26:26 PM UTC-7, Brian Craft wrote: >> >> (make-array (.getComponentType (class arr)) n) seems to work. >> >> On Sunday, July 21, 2013 12:22:41 PM UTC-7, Brian Craft wrote: >>> >>> 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. 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