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MathGroup Archive 2002

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Re: Pattern Matching in Lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35561] Re: Pattern Matching in Lists
  • From: Tom Burton <tomburton at earthlink.net>
  • Date: Fri, 19 Jul 2002 06:08:07 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

Here is a straightforward way, but in two steps. First, reform the patterns
into list elements:

w2 = w //. {a___, 1, 0, b___} :> {a, p, b}

Where "p" is any symbol that does not appear in w. Then use Count in the
usual way:

Count[w2, p]

Tom Burton

On 7/18/02 12:18 AM, in article ah5qce$59o$1 at smc.vnet.net, "Anthony Mendes"
<amendes at zeno.ucsd.edu> wrote:

> Hello,
> 
> Suppose w={1,1,1,0,0,1,0,1,0,0,1,0,0}.
> 
> How can I count the number of occurrences of a 1 in w immediately
> followed by a 0 in w?
> 
> I have tried every incarnation of Count[] I can think of; for example,
> 
> Count[w,{___,1,0,___}]
> 
> does not seem to work.  In general, how can I count the number of
> occurrences of a 1 followed by a 0 in a list of 1's and 0's?  Thank you!
> 



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