Re: List concatenation speed

*To*: mathgroup at smc.vnet.net*Subject*: [mg87586] Re: List concatenation speed*From*: Oliver Ruebenkoenig <ruebenko at uni-freiburg.de>*Date*: Mon, 14 Apr 2008 05:40:28 -0400 (EDT)*References*: <ftsd1e$bba$1@smc.vnet.net>

On Sun, 13 Apr 2008, carlos at colorado.edu wrote: > I am building mesh plots that require concatenation of thousands of > Graphics objects into one list for Show[]. This is done by appending > objects as they are created, and there are several ways to do that. > Tested 3 of them for speed using a simple object: > > p=Table[x,{50}]; n=10000; > ClearAll[poly]; poly={}; > Print[Timing[Do[AppendTo[poly,p],{i,1,n}]]]; > ClearAll[poly]; poly={}; > Print[Timing[Do[poly=Append[poly,p],{i,1,n}]]]; > ClearAll[poly]; poly={}; > Print[Timing[Do[poly=Join[poly,{p}],{i,1,n}]]]; > > {5.8395 Second,Null} > {5.7206 Second,Null} > {6.29728 Second,Null} > > Tests were run on version 5.2 on a G5 desktop Mac. I expected Join to > win, > but it didnt. Is there a faster way? > > Carlos, use LISP style. to append to a list it is always quite fast to build a nested list like poly = {poly,p} in a loop and then post process it. In your case (graphic primitives) you to not even need to post process since Graphics can handle nested lists. p = Line[ Table[{ Random[], Random[]}, {nr}] ]; poly4 = List[]; Print[Timing[ Do[poly4 = {poly4, p}, {i, 1, n}]; ]]; {0.012001 Second, Null} Show[Graphics[poly4]] The point is the the post processing is done outside of the loop. In case you need to post process remember that Flatten only flattens to up until a specific head. Like: p = g[ Table[{ Random[], Random[]}, {nr}] ]; poly5 = List[]; Print[Timing[ Do[poly5 = {poly5, p}, {i, 1, n}]; poly5 = Flatten[ poly5 ]; ]]; {0.020002 Second, Null} poly5[[1]] Now, the question I have is why does this performance depend on the symbol name of the head? like in p = h[ Table[{ Random[], Random[]}, {nr}] ]; poly5 = List[]; Print[Timing[ Do[poly5 = {poly5, p}, {i, 1, n}]; poly5 = Flatten[ poly5 ]; ]]; {4.96831 Second, Null} The problem with this is that Polygon seems to be a slow "head" and Line a fast one. But perhaps I am missing something obvious here ;-) hth, Oliver Oliver Ruebenkoenig, <ruebenko AT uni-freiburg.de>

**Follow-Ups**:**Re: Re: List concatenation speed***From:*Daniel Lichtblau <danl@wolfram.com>