如何使用R中函数名的字符串调用函数？

Question

I am trying to call a function with a given string of the function name.

Eg

print(funcList)
[[1]]
`*`

[[2]]
sin

works:

mult <- `*`
mult(5,6)
[1] 30

doesn't work:

func1 <- funcList[[1]]
func1(5,6)

func2 <- funcList[[2]]
func2(1.2)

So is it possible to call all of the functions in the functionList?

Answer 1

Those don't look like strings; that looks like a list of functions. To answer the question posed in your title, see get() . For example, using your list but stored as character strings:

funcList <- list("*", "sin")

we can use get() to return the function with name given by the selected element of the list:

> f <- get(funcList[[1]])
> f
function (e1, e2)  .Primitive("*")
> f(3,4)
[1] 12

An alternative is the match.fun() function, which given a string will find a function with name matching that string:

> f2 <- match.fun(funcList[[1]])
> f2(3,4)
[1] 12

but as ?match.fun tells us, we probably shouldn't be doing that at the prompt, but from within a function.

If you do have a list of functions, then one can simply index into the list and use it as a function:

> funcList2 <- list(`*`, sin)
> str(funcList2)
List of 2
 $ :function (e1, e2)  
 $ :function (x)  
> funcList2[[1]](3, 4)
[1] 12
> funcList2[[2]](1.2)
[1] 0.9320391

or you can save the functions out as interim objects, but there is little point in doing this:

> f3 <- funcList2[[1]]
> f3(3,4)
[1] 12
> f4 <- funcList2[[2]]
> f4(1.2)
[1] 0.9320391

Answer 2

See documentation for do.call .

A quick demonstration:

do.call("rnorm", list(100, 0, 1))

first parameter can be a string literal, or R object, and the second one is list of arguments that are to be matched with provided function formal arguments.

Answer 3

you could also use match.fun

> functionlist <- list("*","sin")
> f <- match.fun(functionlist[[1]])
> f(5,6)
[1] 30