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Re: working with lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113213] Re: working with lists
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 19 Oct 2010 05:54:37 -0400 (EDT)

On 10/18/10 at 5:47 AM, sam.takoy at yahoo.com (Sam Takoy) wrote:

>I'm not very good at working with lists. May I ask for someone to
>work out an example which has several elements of what I need to do.

>What's the best way to write a function f[list] that goes through
>each element of the lest, doubles each element divisible by three
>and reduces each of the following elements by 1. That is

>f[{ 1 2 3 5 7}] is { 1 2 6 4 12 }

 From your description above, I would expect the output to be
{1,2,6,4,6} not {1,2,6,4,12}

If I have this correct then the following does the trick.

In[2]:= {1, 2, 3, 5, 7} /.
   {a__, b_?(Mod[#, 3] == 0 &), c__} :> {a, 2 b, Sequence @@
({c} - 1)}

Out[2]= {1,2,6,4,6}



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