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MathGroup Archive 2002

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Re: Pattern Matching in Lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35565] Re: Pattern Matching in Lists
  • From: Selwyn Hollis <slhollis at earthlink.net>
  • Date: Fri, 19 Jul 2002 06:08:26 -0400 (EDT)
  • References: <ah5qce$59o$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Here's a simple solution. Say you have a list of 0s and 1s named bits. 
Compute bits + 2*RotateRight[bits] and drop the first entry. Then count 
the number of 2s in the result.

      counter10[bits_]:= Count[Drop[bits+2RotateRight[bits],1],2]

--
Selwyn Hollis
slhollis at earthlink.net
http://www.math.armstrong.edu/faculty/hollis




Anthony Mendes 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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