# [R] symbolic manipulations

Peter Dalgaard BSA p.dalgaard at biostat.ku.dk
Sat Apr 7 02:12:03 CEST 2001

```"Jeff Miller" <jdm at xnet.com> writes:

>         > deriv.xsqr   <-   my.deriv(x^2,   x)
>         > deriv.xsqr
>         2 * x
>         >
>
>         My question is, how do I take the derivative of  deriv.xsqr
>         (I want the answer to be 2) ?
>         The naive guess
>
>         > my.deriv(deriv.xsqr,  x)
>         [1] 0
>
>         is obviously wrong.
>
>         I suspect that, to get the derivative I'm looking for, I need to
> pass
>         something like deparse(deriv.xsqr) into my.deriv, but this doesn't
> work
>         either.

I think the cleanest way is

> eval(substitute(my.deriv(f,x),list(f=deriv.xsqr)))
[1] 2

--
O__  ---- Peter Dalgaard             Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics     2200 Cph. N
(*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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```