R: from file import foo as bar

Question

I am looking for a technique that combines the following two questions:

Define all functions in one .R file, call them from another .R file. How, if possible?

The R equivalent of Python from x import y as z

In other words, I want to import a specific function from someone else's .r file. Under a different name.

Answer 1

You can use source as follows:

In test.R script:

test <- function() message("Hello")

Then, source that file using

someone <- new.env()
source("test.R", someone)

To call someone's code, use

someone$test()

If possible, ask that someone to write a R package.

Answer 2

We call source with local=TRUE inside a new function, and return only the needed function:

source1 <- function(path,fun){
  source(path, local= TRUE)
  get(fun)
}

from x import y as z will be written:

z <- source1(x,y) # where y is a string

Example:

# create 'test.R' file in working directory
write("test  <- function(a,b) a + b
      test2 <- function(a,b) a - b",
      "test.R")

new_fun <- source1("test.R","test2")

new_fun
# function(a,b) a - b
# <environment: 0x0000000014873f08>

test
# Error: object 'test' not found

test2
# Error: object 'test2' not found

# clean up
unlink("test.R")

Answer 3

AFAIK there is no such mechanism in R.

Of course you can do

x.R y <- function() {do_something}

z.R source("x.R") z <- y rm(y)

A better options would be to make x.R into a package. Then you simple do z <- x::y

The best solution is to convert both x.R and z.R into packages and use @importFrom x y into package z and don't bother with changing the name of the function.