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