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MathGroup Archive 2005

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Re: Extracting information from lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63353] Re: [mg63323] Extracting information from lists
  • From: "Barthelet, Luc" <lucb at ea.com>
  • Date: Sat, 24 Dec 2005 16:03:00 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

I suspect you already got many answers, but this is one more:

First /@ Cases[
  Transpose[{Most[FoldList[Plus, 1, Length[#] & /@ Split[list]]], 
    Split[list]}]
  , {_, {x__}} /; x == 1]

{3, 6, 10, 16}

-----Original Message-----
From: Tony King [mailto:mathstutoring at ntlworld.com] 
To: mathgroup at smc.vnet.net
Subject: [mg63353] [mg63323] Extracting information from lists

Does anyone know of a function that will allow me to extract the
positions 
of the first elements of runs of similar elements within a list. For 
example, suppose that

list={7,9,1,6,8,1,1,6,5,1,1,1,8,7,6,1,1,1,1,7}

I need a function that will return

{3,6,10,16}

corresponding to the runs {1},{1,1},{1,1,1},{1,1,1,1} within list

Many thanks

Tony 


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