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<ggrothendi...@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.tur...@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@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. >> > ______________________________________________ R-help@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.
