[R] Counterpart for Matlab's 'feval'?

[Prof Brian Ripley]

On Fri, 24 Jun 2005, Fredrik Thuring wrote:

> I've just begun writing a program that searches for the minimum of a
> function with golden section search. In order to do this in a nice way I
> need a function that takes a function name and an argument and returns the
> function value for that argument, i .e just like Matlab's 'feval'. Is
> there any?

Really?  Take a look at the interface for optimize(): in R you almost 
always want to pass the function not its name.

You could use

feval <- function(fn, x) get(fn)(x)

but it would be rather inefficient to keep looking up the function (and 
there are scoping issues to consider here).

You could also use do.call(fn, list(x)), but that is even less direct.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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