Re: reducing the time of constructing a List
- To: mathgroup at smc.vnet.net
- Subject: [mg57546] Re: reducing the time of constructing a List
- From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
- Date: Wed, 1 Jun 2005 06:01:30 -0400 (EDT)
- Organization: Uni Leipzig
- References: <d7haeo$3pa$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
a) read in the manual the correct syntax for a
For[] statement
and write it down at least 100 times
b) forget all what you have read about For[] and
Do[] and forget
even that these functions exits
c) try
lst1 = If[# == 1, 1, 0] & /@ dat; // Timing
{0.031 Second, Null}
Regards
Jens
<marloo3 at mail15.com> schrieb im Newsbeitrag
news:d7haeo$3pa$1 at smc.vnet.net...
> please, what is the best way to reduce the
> timing of the following lines, the
> source of data is:
> dat = Table[Random[Integer, {0, 10}], {100000}];
> and the purpose is to construct the List lst in
> the following way:
> For[i = 1, i <= 100000,
> If [dat[[i]] == 1,
> lst = Join[lst, {1}], lst = Join[lst,
> {0}]]; i++]; // Timing
>
> Out[]= {226.07 Second, Null}
> on the P4 celeron 2 Ghz , memory 382 MB ram
> thanks
>