How to create a function that attaches the input to the end of an existing string in the function?-CodePudding

Let's say I have this function:

f <- function(input){
  name <- "hello_"
  }

I want to be able to use

f(world)

and have name be renamed to "hello_world".

Important is that I don't want the input to be a string. So the solution should not involve f("world").

CodePudding user response：

Use substitute like this:

f <- function(input) paste0("hello_", substitute(input))
f(world)
## [1] "hello_world"

Note that designing your functions to use nonstandard evaluation (NSE) in this way will make them less flexible for programming. For example, suppose we store "world" in x. Then we get the following which is clearly not what is wanted.

x <- "world"
f(x)
## [1] "hello_x"

It is possible to get around it but it is painful:

do.call("f", list(x))
## [1] "hello_world"