R: Source Function by Name/Import Subset of Functions

====================================================================

R provides a powerful way to manage and import functions from source files. The source function is used to load a script file into the current R environment, but it can be cumbersome when dealing with large scripts or when you need to import specific functions only. In this article, we will explore how to use the source function by name and import subsets of functions in R.

Introduction

R is an interpreted language, which means that scripts are executed line-by-line. When you use the source function to load a script file, it executes all the lines in the file as if they were part of your current code. However, this can lead to issues when dealing with large scripts or when you need to import specific functions only.

The Problem

In the provided Stack Overflow question, the user has a R script named “functions.R” that contains multiple functions. They are currently using the source function to load the entire script into their current environment, which can lead to issues with function naming conflicts and namespace pollution.

Solution Overview

To address this issue, we will introduce two new functions: LoadFunction and UnloadFunction. These functions provide a way to import specific functions from a source file without loading the entire script. We will also explore an alternative approach using the LoadFunction2 and UnloadFunction2 functions.

Using LoadFunction

The LoadFunction function takes two arguments: the path to the source file and the names of the functions to import. It uses the insertSource function from R’s standard library to add the specified functions to the current environment. The eval(parse(text=paste(x," <- function(x) {0}",sep=""))) line is used to create an anonymous function that loads the imported function into the current environment, while suppressing any errors.

LoadFunction <- function(file,...) {
  dots <- match.call(expand.dots = FALSE)$...
  dots <- sapply(dots, as.character)

  output <- lapply(dots, function(x,file){
    eval(parse(text=paste(x," &lt;- function(x) {0}",sep="")),envir = .GlobalEnv)
    suppressMessages(insertSource(file, functions=x))
    eval(parse(text=paste(x," &lt;- ",x,"@.Data",sep="")),envir = .GlobalEnv)
  },file=file)

  return(output)
}

To use this function, you would call it with the path to your source file and the names of the functions to import:

LoadFunction(file="C:\\functions.R",mult,divide)

Using UnloadFunction

The UnloadFunction function takes one argument: the name(s) of the function(s) to unload. It uses the rm function from R’s standard library to remove the specified functions from the current environment.

UnloadFunction <- function(...) {
  dots <- match.call(expand.dots = FALSE)$...
  dots <- sapply(dots, as.character)

  output <- lapply(dots, function(x,file){
    eval(parse(text=paste("rm(",x,",envir = .GlobalEnv)",sep="")))
  },file=file)

  return(output)
}

To use this function, you would call it with the name(s) of the functions to unload:

UnloadFunction(mult,divide)

Alternative Approach Using LoadFunction2 and UnloadFunction2

Alternatively, you can create two new functions: LoadFunction2 and UnloadFunction2. These functions take a different approach by using the eval(parse(text=paste(function_name," <- function(x) {0}",sep=""))) line to load the specified function into the current environment, while suppressing any errors.

LoadFunction2 <- function(file,function_name) {
  eval(parse(text=paste(function_name," &lt;- function(x) {0}",sep="")),envir = .GlobalEnv)
  suppressMessages(insertSource(file, functions=function_name))
  eval(parse(text=paste(function_name," &lt;- ",function_name,"@.Data",sep="")),envir = .GlobalEnv)

}

UnloadFunction2 <- function(function_name) {
  eval(parse(text=paste("rm(",function_name,",envir = .GlobalEnv)",sep="")))
}

To use these functions, you would call them with the path to your source file and the name of the function to import:

LoadFunction2(file="C:\\functions.R","mult")
LoadFunction2(file="C:\\functions.R","divide")
UnloadFunction2("mult")
UnloadFunction2("divide")

Conclusion

R provides a powerful way to manage and import functions from source files. The source function can be cumbersome when dealing with large scripts or when you need to import specific functions only. In this article, we explored two new functions: LoadFunction and UnloadFunction, which provide a way to import specific functions from a source file without loading the entire script. We also introduced an alternative approach using the LoadFunction2 and UnloadFunction2 functions. By using these functions, you can improve your code organization and reduce namespace pollution.

Example Use Cases

Here are some example use cases for the LoadFunction, UnloadFunction, LoadFunction2, and UnloadFunction2 functions:

# Load a script with multiple functions
LoadFunction(file="C:\\functions.R",mult,divide)
print(mult())  # prints the result of the mult function
print(divide(10,2))  # prints the result of the divide function

# Unload a function
UnloadFunction(mult,divide)

# Load a specific function from a script
LoadFunction2(file="C:\\functions.R","mult")
result <- multiply(10,2)
print(result)  # prints the result of the multiply function

Note that these functions are not part of R’s standard library and should be used as a last resort to improve your code organization.

Last modified on 2023-09-15