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Re: Style Question: The Functional Way

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115823] Re: Style Question: The Functional Way
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 21 Jan 2011 04:35:22 -0500 (EST)

DeltaList[L_] := Subtract @@@ Reverse /@ Partition[L, 2, 1]

data = Array[x, 10];

The simplest way is to just use Differences or ListCorrelate.

DeltaList[data] ==
 Differences[data] ==
 ListCorrelate[{-1, 1}, data] ==
 Most[RotateLeft[data] - data] ==
 ({-1, 1}.# & /@ Partition[data, 2, 1])

True


Bob Hanlon

---- Just A Stranger <forpeopleidontknow at gmail.com> wrote: 

=============
Hello,

So I'm trying to learn how to do things the functional way. As an exercise
I'm trying to program a simple economics related table that gives revenue,
marginal revenue, etc given a demand schedule (2 lists of numbers
representing quantity and price respectively). A simple task in a
spreadsheet.

The point is that I need a list of the differences in the given lists, from
which I will be using to get marginal values (derivatives). I'll call it,
say, DeltaList, and I was wondering if this would be a proper "functional"
way to go about the task:




In[0]: DeltaList[L_] := Subtract @@@ Reverse /@ Partition[L, 2, 1]

(DelatList: list -> list)


Basically, it partitions the list into ordered pairs, reverses those ordered
pairs to prep them for the subsequent Subtract application.

Is this the right way to think about this (painfully simple) problem in a
functional way?

Thank you. All of you have been most helpful in the past.




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