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How can I assign the result of an operation from within a function to the global environment?
I have a function that which does some calculations. I would like to assign the result of the function to the global environment from within the function, how do I proceed?
A minimal example:
meanFUN <- function(x) {
mean(x, na.rm = TRUE)
}
How can I assign the result from mean(x, na.rm = TRUE) from within the function to the global environment?
2 answers
In order to assign a variable to the global environment from within a function, there are two ways to proceed: either using the assign operator <<- or using assign().
<<- comes with the following behaviour: It goes through all environments until it finds the variable in question and replaces it with the current value or creates it anew if it's not found. (Everything run in R 4.0.)
> global_x <- 1
> global_x
[1] 1
> meanFUN <- function(x) {
+ global_x <<- mean(x, na.rm = TRUE)
+ }
> meanFUN(c(1:5))
> global_x
[1] 3
This will create a new variable called global_x in the global environment from which it can be accessed and global_x will be changed each time the function is run. However, if global_x is found in an environment before the global environment, it will be changed there. If we have a function inside a function with the same variable name across different environments and use the <<- operator, <<- will only change the first occurrence of the variable in question, so to speak in the overarching local environment of the outer function and not in the global environment.
> global_x <- 1
> global_x
[1] 1
> meanFUN <- function(x) {
+ global_x <- 100
+
+ insideFunction <- function(x) {
+ local_x <- mean(x, na.rm = TRUE)
+ assign("global_x", local_x, envir = .GlobalEnv)
+ print(global_x)
+ }
+
+ print(global_x)
+ insideFunction(x)
+ }
> meanFUN(c(1:5))
[1] 100
[1] 3
> global_x
[1] 1
>
To avoid mistakes while using <<-, it's better to use assign() which gives precise control over what is assigned where.
> global_x <- 1
> global_x
[1] 1
> meanFUN <- function(x) {
+ global_x <- 100
+
+ insideFunction <- function(x) {
+ global_x <- mean(x, na.rm = TRUE)
+ assign("global_x", global_x, envir = .GlobalEnv)
+ print(global_x)
+ }
+
+ print(global_x)
+ insideFunction(x)
+ }
> meanFUN(c(1:5))
[1] 100
[1] 3
> global_x
[1] 3
On Stack Overflow is a similar question where it's explained in even greater detail: https://stackoverflow.com/a/10904810/3884967.
You need to assign the result to a variable as follows (pay attention to the double less than sign)
meanFUN <- function(x) { gvar <<- mean(x, na.rm = TRUE) }
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