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MathGroup Archive 2007

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Re: Mathematica 6.0 easier for me ... (small review)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76556] Re: [mg76457] Mathematica 6.0 easier for me ... (small review)
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 24 May 2007 05:53:53 -0400 (EDT)
  • References: <200705230859.EAA23180@smc.vnet.net>

On 23 May 2007, at 17:59, Paul at desinc.com wrote:

> If I have
> lis={{1,10},{2,10},...{9,10},{11,20},{12,20}...{19,20}
>
> How do I use functional and/or rule to determine where the second
> number (lis[[i,2]]) jumped from 10 to 20 to 30 and save the pair.
> Assuming there was noise, I only want to store the first 10->20, then
> look for 20->30 and so on.  So in time, I want my search to change as
> I progress through the list.  Any input appreciated!

I am not quite sure if I really understand what you wish to do. But  
if what I think is correct, then it seems easy to do it using rule  
based programming:

FirstJump[lis_, n_, m_] := Flatten[({
     lis} /. {___, {x_, n}, {y_, m}, ___} :> Position[lis, {x, n}])]

For example:


ls={{1,10},{2,10},{9,10},{11,20},{12,20},{19,20},{20,30}};


FirstJump[ls,10,20]

{3}


FirstJump[ls,20,30]

{6}

The above assumes that all the pairs in your list are distinct. If  
they are not, then something more complicated is needed, e.g.:

Clear[FirstJump]

FirstJump[lis_, n_, m_] := Position[Flatten[({lis} /. {a___, {x_, n}, {
     y_, m}, b___} :> {a, $1, $2, b}), 1], $1, 1]

ls = {{1,10}, {2, 10}, {9, 10}, {9, 10}, {11, 20}, {12, 20}, {19,  
20}, {20, 30}};


FirstJump[ls, 10, 20]

{{4}}


Andrzej Kozlowski


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