How to call a function using the character string of the function name in R?

Question

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

E.g.

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.