[R] Combining expressions.

[Gabor Grothendieck]

Actually that gives a "call" object. To get an expression object:

> f <- function(e1, n) as.expression(substitute(e1^n, list(e1 = e1[[1]], n = n[[1]])))
> out <- f(expression(x^2+y^2), expression(n)); out
expression((x^2 + y^2)^n)
> class(out)
[1] "expression"

On Fri, Sep 4, 2009 at 10:59 PM, Gabor
Grothendieck<ggrothendieck at gmail.com> wrote:
> 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
>> ######################################################################
>> Attention:
>> This e-mail message is privileged and confidential. If you are not the
>> intended recipient please delete the message and notify the sender.
>> Any views or opinions presented are solely those of the author.
>>
>> This e-mail has been scanned and cleared by MailMarshal
>> www.marshalsoftware.com
>> ######################################################################
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>