Hi.
I'm looking for an R equivalent to something like function pointers in C/C++.
I have a search procedure that evaluates the fitness of each point it reaches
as it moves along, and decides where to move next based on its fitness
evaluation. I want to be able to pass different fitness functions to this
procedure. I am trying to find a good way to do this. I was thinking of
passing in the name of the function and then using eval. However, I haven't
gotten this to work the way I'd like it to. Consider the following example:
> stu <- function(x) {return( 1 + (2*x*x) - (3*x) )}> (x=0:3)[1] 0 1 2 3>
> stu(x)[1] 1 0 3 10> (fun="stu")[1] "stu"> eval( parse( text = paste( fun,
> "(", x, ")", sep = "" ) ) )[1] 10>
Notice that the function I defined called "stu" will operate on a vector x and
return a vector y = stu(x) such that y[i] equals stu(x[i]). When I tried to
pass stu and x to a procedure that would evaluate stu(x) I only get stu(x[N]),
when N is the last element of x. What am I doing wrong? Is there a better way
to pass function references?
I can get the following to work, but it seems awfully clunky:
> sapply( 1:length(x), function(i){ return( eval( parse( text = paste( fun,
> "(", x[i], ")", sep = "" ) ) ) ) } )[1] 1 0 3 10>
Thanks!
-- TMK --212-460-5430 home917-656-5351 cell
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