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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: [mg76599] Re: Mathematica 6.0 easier for me ... (small review)
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Thu, 24 May 2007 06:16:11 -0400 (EDT)
  • References: <f30vpv$mkn$1@smc.vnet.net>

On May 23, 1:59 am, P... at desinc.com wrote:
> ...
> 4.  At work, I haven't had to resort to other programs because
> Mathematica wasn't the best choice.  This is extremely nice.  BTW,
> There's a "temporal" advantage with procedural programming that hasn't
> been apparant to me in functional or rule.  Still working on it. Maybe
> someone can help.  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!
> ...

lis = {{1,10}, {2,10}, {3,10}, {4,10}, {5,10}, {6,20}, {7,20},
  {8,20}, {9,20}, {10,30}, {11,30}, {12,30}, {13,30}, {14,30},
{15,30}, {16,30}, {17,40}, {18,40}, {19,40}, {20,50}, {21,50}};

Extract[ lis, Position[ Rest@# - Most@# & @ lis[[All,2]], 10 ] ]

{{5,10},{9,20},{16,30},{19,40}}

Two comments:

1. "save the pair" is ambiguous. Which pair? I have returned the
   list of {i,10j} pairs that precede an {i+1,10{j+1)} pair.

2. This can be done faster but less transparently using SparseArray.



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