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Re: reducing the time of constructing a List


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
>

1.2Ghz G4 2GB RAM OSX 10.4.1 Mathematica 5.1

In[69]:=
Timing[First[Last[
      Reap[i = 0; lengthdat =
         Length[dat];
        While[i++ < lengthdat,
         If[dat[[i]] == 1,
          Sow[{1}], Sow[
           {0}]]]]]]; ]
Out[69]=
{1.2697460000000014*Second,
   Null}


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