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Re: AppendTo VERY slow


In a message dated 7/6/02 6:53:23 AM, M.P.Croucher at Sheffield.ac.uk writes:

>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)

Use either

Transpose[{xlist, ylist}]

or

Thread[{xlist, ylist}]


Bob Hanlon
Chantilly, VA  USA


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