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MathGroup Archive 2005

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Re: reducing the time of constructing a List

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57576] Re: reducing the time of constructing a List
  • From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
  • Date: Wed, 1 Jun 2005 06:02:55 -0400 (EDT)
  • Organization: University of Southern Maine
  • References: <d7haeo$3pa$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

here is a simple and fast method:

lst = Table[ If[ dat[[i]] == 1, 1, 0], {i, Length[dat]}]

(Your timing should now be under 0.1 second)

Mariusz




>>> <marloo3 at mail15.com> 05/31/05 5:23 AM >>>
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




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