R help - Nov 2003 - Expressions and Functions

Dear R People:

When the D function is used for a symbolic derivative,
an expression is returned, which is fine.

How do you change that expression to a function, please?

I've been experimenting with substitute and deparse, but no success
yet.

This is R 1.8.0 for Windows.

thanks in advance for the help!

Sincerely,
Erin Hodgess
mailto: hodgess at gator.uhd.edu

Would it work to use deriv with the optional function.arg argument?

In some ways deriv is just a wrapper around repeated calls to D. (It
does a bit more than that but you could think of it that way.)

Erin Hodgess <hodgess at gator.uhd.edu> writes:
> Dear R People:
> 
> When the D function is used for a symbolic derivative,
> an expression is returned, which is fine.
> 
> How do you change that expression to a function, please?
> 
> I've been experimenting with substitute and deparse, but no success
> yet.
> 
> This is R 1.8.0 for Windows.
> 
> thanks in advance for the help!
> 
> Sincerely,
> Erin Hodgess
> mailto: hodgess at gator.uhd.edu
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
-- 
Douglas Bates                            bates at stat.wisc.edu
Statistics Department                    608/262-2598
University of Wisconsin - Madison        http://www.stat.wisc.edu/~bates/

You should be able to use deriv(..., func=TRUE) to get a function returned,
instead of an expression.

If you need to use D, here's a rather clumsy way that seems to work:
> dx2x <- D(expression(x^2), name="x"); dx2x
2 * x
> eval(parse(text=paste("f <- function(x){",
                        paste(deparse(dx2x), collapse=";"),
"}")))
> f
function(x){ 2 * x }

HTH,
Andy
> From: Erin Hodgess [mailto:hodgess at gator.uhd.edu] 
> 
> Dear R People:
> 
> When the D function is used for a symbolic derivative,
> an expression is returned, which is fine.
> 
> How do you change that expression to a function, please?
> 
> I've been experimenting with substitute and deparse, but no 
> success yet.
> 
> This is R 1.8.0 for Windows.
> 
> thanks in advance for the help!
> 
> Sincerely,
> Erin Hodgess
> mailto: hodgess at gator.uhd.edu

I can think of 2 ways:

f <- function(x) { }
body(f) <- D(expression(log(x)), "x")

Or maybe

g <- deriv(expression(log(x)), "x", function.arg = TRUE)
f <- function(x) { attr(g(x), "gradient") }

Or something along those lines.

-roger

Erin Hodgess wrote:
> Dear R People:
> 
> When the D function is used for a symbolic derivative,
> an expression is returned, which is fine.
> 
> How do you change that expression to a function, please?
> 
> I've been experimenting with substitute and deparse, but no success
> yet.
> 
> This is R 1.8.0 for Windows.
> 
> thanks in advance for the help!
> 
> Sincerely,
> Erin Hodgess
> mailto: hodgess at gator.uhd.edu
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>