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.