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Re: reducing the time of constructing a List


You are just replacing non-unit entries in dat by 0. Use functional
programming and forget For statements.

dat = Table[Random[Integer, {0, 10}], {100000}];

lst = If[# == 1, 1, 0] & /@ dat; // Timing
{0.05 Second, Null}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: marloo3 at mail15.com [mailto:marloo3 at mail15.com]
To: mathgroup 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





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