Re: Map and functional constructs to replace iterative
- To: mathgroup at smc.vnet.net
- Subject: [mg96848] Re: [mg96783] Map and functional constructs to replace iterative
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Thu, 26 Feb 2009 07:54:18 -0500 (EST)
- Reply-to: hanlonr at cox.net
percentChange[currentValue_, previousValue_] :=
100*(currentValue - previousValue)/previousValue
data = {v1, v2, v3, v4};
percentChange @@@ Reverse /@ Partition[data, 2, 1]
{(100*(v2 - v1))/v1, (100*(v3 - v2))/v2, (100*(v4 - v3))/v3}
100*ListCorrelate[{-1, 1}, data]/Most[data]
{(100*(v2 - v1))/v1, (100*(v3 - v2))/v2, (100*(v4 - v3))/v3}
% == %%
True
Bob Hanlon
---- Andreas <aagas 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.