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MathGroup Archive 2002

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Re: Newbie Question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32749] Re: [mg32686] Newbie Question
  • From: BobHanlon at aol.com
  • Date: Fri, 8 Feb 2002 03:49:21 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 2/6/02 6:39:26 AM, kbrunsman at ou.edu writes:

>I can't believe that I am asking this question, but ... I'm tired of Fortran
>and find the symbolic part of Mathematica extremely useful.
>
>I have a list with Dimensions = {10,000, 6} and I need to find the Percent
>Difference between items in a column.
>
>I can parse out the column I need using Take [data [[All, Column #]]] ---
>no
>big deal.  So far, so good.
>
>Now here's the problem --- How do I get % Differences between any of 10,000
>items in that list?  I need to take % Differences between adjacent pairs,
>i.e. n and n-1, as well as items n and n-m where m can range from 1 to
>10,000.
>

relativeChange[data_List, m_Integer] :=
 
    (RotateLeft[data,m]-data)/data;

data=Table[ToExpression["x"<>ToString[k]],{k,1,4}];

Percent difference of adjacent elements

100*relativeChange[data,1]

{(100*(x2 - x1))/x1, (100*(x3 - x2))/x2, (100*(x4 - x3))/x3,
 
  (100*(x1 - x4))/x4}

100*relativeChange[data,-1]

{(100*(x4 - x1))/x1, (100*(x1 - x2))/x2, (100*(x2 - x3))/x3,
 
  (100*(x3 - x4))/x4}

Percent difference of elements offset by m

100*relativeChange[data,3]

{(100*(x4 - x1))/x1, (100*(x1 - x2))/x2, (100*(x2 - x3))/x3,
 
  (100*(x3 - x4))/x4}

100*relativeChange[data,-3]

{(100*(x2 - x1))/x1, (100*(x3 - x2))/x2, (100*(x4 - x3))/x3,
 
  (100*(x1 - x4))/x4}


Bob Hanlon
Chantilly, VA  USA


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