# Re: [R] how to get f(x)=___ from a piecwise function

From: jim holtman <jholtman_at_gmail.com>
Date: Sun 26 Feb 2006 - 16:27:48 EST

?approxfun

> x<- c(-100.4, 32.0, 99.8, 200.2, 300.6, 399.8, 500.0, 600.0, 699.6, 799.6,
+ 899.8)
> y<- c(0.4, 0.0, 0.2, -0.2, -0.6, 0.2, 0.0, 0.0, 0.4, 0.4, 0.2)
> x.f <- approxfun(x,y)
> x.f(356)

[1] -0.1532258

On 2/25/06, Eric C. Jennings <matheric@u.washington.edu> wrote:
>
> >From actual real-world readings, I have two vectors:
>
> x<- c(-100.4, 32.0, 99.8, 200.2, 300.6, 399.8, 500.0, 600.0, 699.6, 799.6,
> 899.8)
> y<- c(0.4, 0.0, 0.2, -0.2, -0.6, 0.2, 0.0, 0.0, 0.4, 0.4, 0.2)
>
> which, in the usual way constitute a continuous piecewise function.
>
> What I want to do is find an easy method to get at f(x) for some x I have
> NOT specified in the above vector. For example I want f(356).
>
> I have already put the time and effort in to write a program to compute
> this
> by breaking the function into the various pieces and computing the slopes
> of
> the individual lines etc. etc.
>
> I am just looking to find an easier method.
>
> Thank you for your help.
> Eric
>
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```--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What the problem you are trying to solve?

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