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MathGroup Archive 2006

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Re: List manipulation question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67195] Re: [mg67163] List manipulation question
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 11 Jun 2006 23:08:02 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

dif[x_?VectorQ]:=Join[{x[[2]]-x[[1]]},
      ListConvolve[{1/2,0,-1/2},x],
      {x[[-1]]-x[[-2]]}];

list={x1,x2,x3,x4};

dif[list]

{x2 - x1, x3/2 - x1/2, x4/2 - x2/2, x4 - x3}

list={3700,3800,3900,3950,4000,
      4050,4100,4150,4200,4250,
      4300,4350,4400,4450,4500,
      4550,4600,4650};

dif[list]

{100,100,75,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50}


Bob Hanlon

---- LectorZ <lectorz at mail.ru> wrote: 
> Dear experts,
> 
> I need to calculate distances between the elements of the following
> list:
> 
> list={3700, 3800, 3900, 3950, 4000, 4050, 4100, 4150, 4200, 4250, 4300,
> 4350,
> 4400, 4450, 4500, 4550, 4600, 4650}
> 
> with the following logic:
> 
> a) If it is the first element, then take the simple difference to the
> next (i.e. 3800 - 3700)
> b) If it is the last element, then take the simple difference to the
> second last (i.e. 4650 -4600)
> c) the difference for all elements in between shoud be calculated as
> (next - last)/2 (i.e. (3900 - 3700)/2)
> 
> This list should come out as a result:
> 
> result={100,100,75,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50}
> 
> Thanks a lot for your help
> 
> LZ
> 


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