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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: [mg76586] Re: [mg76457] Mathematica 6.0 easier for me ... (small review)
  • From: János <janos.lobb at yale.edu>
  • Date: Thu, 24 May 2007 06:09:26 -0400 (EDT)
  • References: <200705230859.EAA23180@smc.vnet.net>

> 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!

Here is a newbie approach:

In[36]:=
lst = Table[{Random[Integer,
       {1, 100}], Random[
       Integer, {9, 31}]},
     {i, 1000}];

In[37]:=
ctl = {10, 20, 30, 40};

In[40]:=
First[Last[Reap[i = 1; j = 1;
      While[i <= Length[lst],
       If[lst[[i,2]] ==
          ctl[[j]],
         Sow[{i, lst[[i]]}];
          j++; , Null];
        i++; ]]]]
Out[40]=
{{3, {99, 10}},
   {115, {49, 20}},
   {127, {20, 30}}}

First part of an element show what position the element occurred in 
lst, the second part is the element itself.

J=E1nos


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