# [R] interpolation and numerical differentiation in R ?

Douglas Bates bates at stat.wisc.edu
Sun Sep 2 00:38:46 CEST 2001

```"Robert D. Merithew" <merithew at ccmr.cornell.edu> writes:

> Hi,
>
> I'm trying to determine if R is useful to me.  I've browsed 'The Basics of
> S and S-Plus' (Krause & Olson), and like the logic of the language.
> However, I don't see an easy way to do things like this:
>
>
> * given a set of observations (x,y) (x and y equal-length vectors), and a
> 2nd set of abscissas x2, interpolate y at the new abscissas x2.  (for now,
> I don't really care what kind of interpolation -- linear, some type of
> spline, etc.)

See interpSpline in the splines library.

> * given observations (x,y), (with unequally-spaced x), create vector z
> with the numerical derivative of y with respect to x (eg evaluated at the
> values x).

When evaluating the interpolating spline produced by interpSpline you
can specify that you want derivatives instead of the function value.
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```