[R] Partial Function Application

[David Winsemius]

On Aug 6, 2010, at 9:56 AM, Mog wrote:

> Hi. I would like to partially apply a function to a list of arguments,
> and I don't know how to do this in R, without perhaps writing default
> values to the formals() of my function, or writing to the environment
> object of a function. For context, my definition of partially apply
> is: "fix some of the arguments, leaving the others as variables,
> return a new function that takes the un-fixed arguments from the
> original function as arguments"

I don't understand the difficulties:

 > f1 <- function(a,b,c,d) a+b+c+d
 > f1(1,2,3,4)
[1] 10

 > f2 <- function(a , b) f1(a,b, 3,4)
 > f2(1,2)
[1] 10

 > f1(1,2)
Error in a + b + c : 'c' is missing

 > floop <- function(a,b){ for( cc in 2:4) { for (dd in 5:7)  
{ print( f1(a, b, cc, dd) )}} }
 > floop(1,2)
[1] 10
[1] 11
[1] 12
[1] 11
[1] 12
[1] 13
[1] 12
[1] 13
[1] 14
>
> The issue is that I would like several different sets of arguments for
> the "partially applied" phase, and I think that would involve copying
> the function to several different places with the above methods.
>
> Alternately, I could hard-code the partial applications using a
> function() form, but I would prefer not to do this, as there will be a
> sizable number of these closures needed and I'd prefer to automate the
> process.
>
> Thanks!
>
> --Mog
>
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David Winsemius, MD
West Hartford, CT