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MathGroup Archive 2006

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Re: List manipulation question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67205] Re: List manipulation question
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Sun, 11 Jun 2006 23:08:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 6/11/06 at 2:17 AM, lectorz at mail.ru (LectorZ) wrote:

>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}

Your c) doesn't quite make sense to me. 3700 appears once as the first element. I don't see how to equate 3700 with "last". 

In any case, I can get the same result as you show with

In[19]:=
Flatten@{-Subtract@@Take[list,2],Subtract@@@Partition[list,3,1][[
    All,{3,1}]]/2,-Subtract@@Take[list,-2]}

Out[19]=
{100,100,75,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50}
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