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Re: Map and functional constructs to replace iterative statements

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96854] Re: Map and functional constructs to replace iterative statements
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Thu, 26 Feb 2009 07:55:23 -0500 (EST)
  • References: <go31ba$f47$1@smc.vnet.net>

Look at Gergory's question "Series of Percentage Changes" that by a
cosmic coincidence appeared today. It seems to answer your question.

But the following will also work

-100* Subtract[##]/#1& @@@  Partition[timeSeries, 2, 1]

Perhaps you should check for zero divisions.

Cheers -- Sjoerd

On Feb 25, 11:00 am, Andreas <aa... at ix.netcom.com> wrote:
> I have begun to replace Table, Do, While, or For, but in my thinking with Map, Inner, Outer and other functional programming constructs as I learn more about Mathematica.
>
> But, I'm stuck.  I need to figure out how to use Map (or some related approach) when a function needs both a current value and a previous value in a time series, such as a percentage change function (or perhaps more generally stated, when I need to refer to previous values in a series or even previous calculations).  But first a simple case:
>
> percentChange[currentValue_, previousValue_] := 100 * ( currentValue - previousValue) / previousValue
>
> I know how to apply this iteratively, but how can I do it with Map or some other functional construct?
>
> Say I have a list: timeSeries
>
> I thought to try something like this:
>
> Map[percentChange[?,?], timeSeries]
>
> but I don't know how what to put in for "?".
>
> Any help much appreciated.
>
> Thx.



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