Re: AppendTo VERY slow
- To: mathgroup at smc.vnet.net
- Subject: [mg35330] Re: [mg35279] AppendTo VERY slow
- From: jmt <jmt at agat.net>
- Date: Mon, 8 Jul 2002 03:20:12 -0400 (EDT)
- References: <200207060944.FAA11921@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
This should be faster
outlist = {};
Do[
elem = {xlist[[count]], ylist[[count]]};
outlist = {outlist, elem},
{count, number}];
Drop[Flatten[outlist, number - 1], 1]
See notes in HelpBrowser for AppendTo :
An alternative and often more efficient way to build up a list is to use a
sequence of assignments of the form
s ={s, elem} and then to call Flatten on the resulting structure.
On Saturday 06 July 2002 11:44, Mike wrote:
> 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
- References:
- AppendTo VERY slow
- From: M.P.Croucher@Sheffield.ac.uk (Mike)
- AppendTo VERY slow