[R] Combining expressions.

[Gabor Grothendieck]

Use substitute:

> f <- function(e1, n) substitute(e1^n, list(e1 = e1, n = n[[1]]))
> f(expression(x^2+y^2), expression(n))
expression(x^2 + y^2)^n

On Fri, Sep 4, 2009 at 10:22 PM, Turner Rolf<r.turner at auckland.ac.nz> wrote:
>
> I am trying to construct a function to which I pass an expression as an argument.
> >From that expression I want to create a somewhat more complicated expression
> and then differentiate it using D() or deriv().
>
> To give a simple example, I'd like to be able to do something like
>
> e1 <- expression(x^2 + y^2)
> e2 <- some.magic(e1,"n")
>
> or maybe e2 <- some.magic(e1,expression(n))
>
> and get e2 being expression((x^2+y^2)^n).  (Whence I can then do D(e2,"x") and D(e2,"y").)
>
> Is there any way to accomplish this?
>
> Thanks.
>
>        cheers,
>
>         Rolf Turner
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