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Re: Pure functions and Select[] sequential elements of list

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I agree that this kind of functionality is not easily accessed in Mathematica.  It seems to be a common need that requires some obscure formulation to get the needed effect, at least so far as I have figured out. Here are two examples of what I use:

1. I sometimes use Partition[...] first to get this effect:

mList  Partition[{1, 2, 3, 4, 5, 7, 6, 8}, 2, 1];
First /@ Select[mList, (#[[1]] > #[[2]]) &]

2. Pattern matching can also do the trick, though can be slow depending on the size of your task.

mList = {1, 2, 3, 4, 5, 7, 6, 8};
ReplaceList[mList, Rule[{___, firstValue: _, secondValue: _, ___} /; (firstValue> secondValue), firstValue]]



________________________________________
From: McHale, Paul [Paul.McHale@excelitas.com]
Sent: Sunday, May 29, 2011 07:38
Subject:  Pure functions and Select[] sequential elements of list

Hi,

Does anyone know of a way to use a pure function to access current and next element of list with uses like Select[]?  I know I might be dazed and confused, but I thought there was a way.  I.e.

mList={1,2,3,4,5,7,6,8};
Select[mList, (#? > #??)&]

Where #? Is element N and #?? Is element N+1.  I would expect the previous code (assuming N?, N?? were valid) to return 7.

Maybe there is no way to do this with a pure function.  I know there are many other ways.  This would be one more way to not require a looping construct to resolve this.  If someone knows of straightforward ways other than Table[] or For[], Do[]... looping contructs, I would appreciate it the general knowledge.  I constantly struggle against my C language beginning ;)

Best Regards,
Paul


Paul McHale  |  Electrical Engineer, Energetics Systems  |  Excelitas Technologies Corp.

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Re: Pure functions and Select[] sequential elements of list "Scot T. Martin" <smartin@seas.harvard.edu> - 2011-05-30 10:36 +0000

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