How should I go about when creating a function that should return a function that includes an argument of the original function?
Consider for instance this function:
a <- function(value){
function(x) x + value
}
I'd like it to return the value I specify in the parameter in the resulting function, like this:
b <- a(3)
#> b
#> function(x) x + 3
And be able to use the resulting function b thereafter:
b(2)
#[1] 5
Instead, I get:
> b
function(x) x + value
<environment: 0x000002254f80a758>
I've tried using substitute, eval, parse... but I'm a bit confused. Preferably a base R solution.
As I discussed in the comments the function shown in the question already works so the approaches below are not really needed but if you want to create a function with the value of value hard coded into it then one of these. No packages are used.
1) do.call/substitute
a <- function(value, envir = parent.frame()) {
f <- function(x) x + value
body(f) <- do.call("substitute", list(body(f), list(value = value)))
environment(f) <- envir
f
}
b <- a(3)
b
## function (x)
## x + 3
b(4)
## [1] 7
lapply(1:3, a, envir = environment())
giving:
[[1]]
function (x)
x + 1L
[[2]]
function (x)
x + 2L
[[3]]
function (x)
x + 3L
2) strings Another possibility is to use string substitution:
a2 <- function(value, envir = parent.frame()) {
eval(parse(text = gsub("\\bvalue\\b", value, "function(x) x + value")), envir)
}
lapply(1:3, a2, envir = environment())
giving:
[[1]]
function(x) x + 1
[[2]]
function(x) x + 2
[[3]]
function(x) x + 3