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MathGroup Archive 2002

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AppendTo VERY slow

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35279] AppendTo VERY slow
  • From: M.P.Croucher at Sheffield.ac.uk (Mike)
  • Date: Sat, 6 Jul 2002 05:44:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I use lists a lot in mathematica and tend to use AppendTo[] a lot in
my programs.  Recently I wrote a function that i call over and over
again and found that the results were coming very slowly and i MEAN
slowly.  I was doing Fourier Transforms and all kinds of stuff so I
put it down to those at first but I have just put in a load of Print
statements just after each part of the function to see what was taking
so long.

I was amazed to see that the Fourier Transforms were so quick and what
was actually taking the time was a part of my function that collected
the results togther in the form I wanted and outputted the result.  It
looks like this

Do[
    	elem = {xlist[[count]], ylist[[count]]]};
    	AppendTo[outlist, elem];
     , {count, 1, number}
    ];

It seems that as the list grows it gets slower and slower.  Any tips
on a way around this would be greatly appreciated (would speed my life
up no end)


Thank

Mike


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