Re: working with lists

*To*: mathgroup at smc.vnet.net*Subject*: [mg113224] Re: working with lists*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Tue, 19 Oct 2010 05:56:41 -0400 (EDT)*References*: <201010180947.FAA00936@smc.vnet.net>

This uses pattern matching and recursion so it won't be particularly fast, but it seems to me the easiest way to program this sort of thing: f[ls_List] /; ! MemberQ[Mod[ls, 3], 0] := ls f[ls_List] := ls /. {v___, u_ /; Mod[u, 3] == 0, w___} :> Flatten[{{v, 2 u}, f[{w} - 1]}] In[5]:= f[{1,2,3,5,7}] Out[5]= {1,2,6,4,12} In[4]:= f[{1, 2, 3, 5, 7, 11, 12, 13, 14}] Out[4]= {1,2,6,4,12,18,18,18,18} Andrzej Kozlowski On 18 Oct 2010, at 11:47, Sam Takoy wrote: > Hi, > > 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 } > > Many thanks in advance, > > Sam >

**References**:**working with lists***From:*Sam Takoy <sam.takoy@yahoo.com>