Re: reducing the time of constructing a List

*To*: mathgroup at smc.vnet.net*Subject*: [mg57571] Re: reducing the time of constructing a List*From*: Curt Fischer <tentrillion at gmail.NOSPAM.com>*Date*: Wed, 1 Jun 2005 06:02:30 -0400 (EDT)*References*: <d7haeo$3pa$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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 Use pattern matching in some way or other! That should be much faster than procedural programming. I don't know my laptop specs offhand but it has a slower processor and perhaps slightly more memory than your machine. In[1]:= dat=Table[Random[Integer,{0,10}],{100000}]; In[2]:= ans1=(dat/.n_Integer-> If[n\[Equal]1,1,0]);//Timing Out[2]= {0.441 Second,Null} In[3]:= ans2=(dat/.n_?(#!=1&)-> 0);//Timing Out[3]= {0.28 Second,Null} In[4]:= ans1==ans2 Out[4]= True -- Curt Fischer