Dear list
# I have a function
ff <- function(a,b=2,c=4){a+b+c}
# which I programmatically want to modify to a more specialized function in
which a is replaced by 1
ff1 <- function(b=2,c=4){1+b+c}
# I do as follows:
vals <- list(a=1)
(expr1 <- as.expression(body(ff)))
expression({
a + b + c
})
(expr2 <- do.call("substitute", list(expr1[[1]], vals)))
{
1 + b + c
}
# This "works",
eval(expr2, list(b=10,c=12))
[1] 23
# - but I would like a function. Hence I do:
ll <- alist(b=, c=, eval(expr2))
ff2 <- as.function(ll)
ff2(b=10,c=12)
[1] 23
# BUT I am only half-way where I want to be because the alist(b=, c=, ...)
# requires me plugin the remaining formals by hand. I do:
newformals <-setdiff(names(formals(ff)), names(vals))
vv <- vector("list", length(newformals))
names(vv) <- newformals
(hh <- c(vv, expr2))
$b
NULL
$c
NULL
[[3]]
{
1 + b + c
}
(ff3 <- as.function(hh))
function (b = NULL, c = NULL)
{
1 + b + c
}
ff3(10,12)
[1] 23
# Hence I get the function that returns what I want (given the correct input)
# but the arguments will have default values that I don't want.
# I want to retain the original default values (if any)
ff1()
[1] 7
ff3()
numeric(0)
I have two questions:
1) How to fix the above?
2) Aren't there more elegant alternatives?
Any help would be appreciated.
Regards
S?ren
Hi,
Is it what you are looking for?
> ff <- function(a,b,c){a+b+c}
> ff(1,10,12)
[1] 23
> ff(589,2,4)
[1] 595
HTH,
Pascal
Le 04/02/2013 19:00, S?ren H?jsgaard a ?crit :> Dear list
>
> # I have a function
> ff <- function(a,b=2,c=4){a+b+c}
> # which I programmatically want to modify to a more specialized function in
which a is replaced by 1
> ff1 <- function(b=2,c=4){1+b+c}
>
> # I do as follows:
> vals <- list(a=1)
> (expr1 <- as.expression(body(ff)))
> expression({
> a + b + c
> })
> (expr2 <- do.call("substitute", list(expr1[[1]], vals)))
> {
> 1 + b + c
> }
>
> # This "works",
> eval(expr2, list(b=10,c=12))
> [1] 23
>
> # - but I would like a function. Hence I do:
> ll <- alist(b=, c=, eval(expr2))
> ff2 <- as.function(ll)
> ff2(b=10,c=12)
> [1] 23
>
> # BUT I am only half-way where I want to be because the alist(b=, c=,
...)
> # requires me plugin the remaining formals by hand. I do:
> newformals <-setdiff(names(formals(ff)), names(vals))
> vv <- vector("list", length(newformals))
> names(vv) <- newformals
> (hh <- c(vv, expr2))
> $b
> NULL
> $c
> NULL
> [[3]]
> {
> 1 + b + c
> }
>
> (ff3 <- as.function(hh))
> function (b = NULL, c = NULL)
> {
> 1 + b + c
> }
> ff3(10,12)
> [1] 23
> # Hence I get the function that returns what I want (given the correct
input)
> # but the arguments will have default values that I don't want.
> # I want to retain the original default values (if any)
> ff1()
> [1] 7
> ff3()
> numeric(0)
>
> I have two questions:
> 1) How to fix the above?
> 2) Aren't there more elegant alternatives?
>
> Any help would be appreciated.
> Regards
> S?ren
>
>
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>
On Mon, Feb 4, 2013 at 5:00 AM, S?ren H?jsgaard <sorenh at math.aau.dk> wrote:> Dear list > > # I have a function > ff <- function(a,b=2,c=4){a+b+c} > # which I programmatically want to modify to a more specialized function in which a is replaced by 1 > ff1 <- function(b=2,c=4){1+b+c} >This a currying operation. Try: library(functional) ff1 <- Curry(ff, a = 1) # test identical(ff1(2, 4), ff(1, 2, 4)) # TRUE -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com