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Re: List concatenation speed

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87585] Re: List concatenation speed
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 14 Apr 2008 05:40:16 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <ftsd1e$bba$1@smc.vnet.net>

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?

Hi Carlos,

On my system (v6.0.2 Intel 64-bit Mac OS X 1.5.2), using *Sow* and 
*Reap* as in

     Reap[Do[Sow[p], {i, 1, n}]][[2, 1]]

is more than 80 times faster than your fastest solution. This will not 
work on version below 5.xx.

Using *Table* is about 35 faster and works on any version.

     Table[p, {i, 1, n}]

Here are the timings for the five approaches:

     p = Table[x, {50}]; n = 10000;
     ClearAll[poly1]; poly = {};
     Print[Timing[poly = Reap[Do[Sow[p], {i, 1, n}]][[2, 1]];]];
     ClearAll[poly]; poly = {};
     Print[Timing[poly = Table[p, {i, 1, n}];]];
     ClearAll[poly]; poly = {};
     Print[Timing[Do[poly = Append[poly, p], {i, 1, n}]]];
     ClearAll[poly]; poly = {};
     Print[Timing[Do[AppendTo[poly, p], {i, 1, n}]]];
     ClearAll[poly]; poly = {};
     Print[Timing[Do[poly = Join[poly, {p}], {i, 1, n}]]];


     {0.00965,Null}

     {0.025739,Null}

     {0.828765,Null}

     {0.848818,Null}

     {1.10683,Null}

Best regards,
-- Jean-Marc



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