Re: reducing the time of constructing a List

*To*: mathgroup at smc.vnet.net*Subject*: [mg57561] Re: reducing the time of constructing a List*From*: "Carl K. Woll" <carlw at u.washington.edu>*Date*: Wed, 1 Jun 2005 06:01:55 -0400 (EDT)*Organization*: University of Washington*References*: <d7haeo$3pa$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

<marloo3 at mail15.com> wrote in message news:d7haeo$3pa$1 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 > You forgot to initialize lst in your post. At any rate, using For is not recommended. Instead, try to make use of operations that are listable: 1-Abs[Sign[dat-1]] evaluates in 0 seconds on my machine and yields the same answer. Carl Woll