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MathGroup Archive 1996

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Re: functional code

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4807] Re: functional code
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Mon, 16 Sep 1996 23:51:28 -0400
  • Organization: University of Western Australia
  • Sender: owner-wri-mathgroup at wolfram.com

richard j. gaylord wrote:
 
> Given a list of numbers row={18,19,1,11,25,12,22,14}
> Select the numbers from the list by taking the largest number
> from the ends of the list  until the list is empty.

Here are two straightforward pattern-matching solutions:
 
In[1]:= row={18,19,1,11,25,12,22,14};

In[2]:= {{},row}//.{{d___},{a_,b___,c_}}:>
	{{d,Max[a,c]},If[a<c,{a,b},{b,c}]}//Flatten

Out[2]= {18, 19, 14, 22, 12, 25, 11, 1}

In[3]:= {{},row}//.{
	{{d___},{a_,b___,c_}}/;a<c  :> {{d,c},{a,b}},
	{{d___},{a_,b___,c_}}/;a>=c :> {{d,a},{b,c}}}//Flatten

Out[3]= {18, 19, 14, 22, 12, 25, 11, 1}

Cheers,
	Paul 
_________________________________________________________________ 
Paul Abbott
Department of Physics                       Phone: +61-9-380-2734 
The University of Western Australia           Fax: +61-9-380-1014
Nedlands WA  6907                         paul at physics.uwa.edu.au 
AUSTRALIA                           http://www.pd.uwa.edu.au/Paul

          Black holes are where God divided by zero
_________________________________________________________________

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