Re: reducing the time of constructing a List
- To: mathgroup at smc.vnet.net
- Subject: [mg57565] Re: [mg57533] reducing the time of constructing a List
- From: Sseziwa Mukasa <mukasa at jeol.com>
- Date: Wed, 1 Jun 2005 06:02:11 -0400 (EDT)
- References: <200505310900.FAA03434@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On May 31, 2005, at 5:00 AM, marloo3 at mail15.com wrote:
> 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
Here's one way:
Timing[dat /. {0 -> 0, 1 ->
1, 2 -> 0, 3 -> 0, 4 -> 0, 5 -> 0, 6 -> 0, 7 -> 0, 8 -> 0, 9 -
> 0,
10 -> 0};]
which results in
{0.065167 Second, Null}
on a 2.7GHz G5 PowerMac.
Later,
Ssezi