Re: List concatenation speed
- To: mathgroup at smc.vnet.net
- Subject: [mg87617] Re: List concatenation speed
- From: dh <dh at metrohm.ch>
- Date: Mon, 14 Apr 2008 05:46:21 -0400 (EDT)
- References: <ftsd1e$bba$1@smc.vnet.net>
Hi Carlos, with Append & Co. every time you add a new element, the whole list is copied. To prevent this, you may build a nested list like e.g.: poly={poly,p} instead of using Append. Finally you may Flatten the list: Flatten[poly]. hope this helps, Daniel 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? >