CODEWITHSUNDEEP
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Joezerz
Joezerz

Reputation: 151

Parameter object within R package

I have a simulation model that takes parameters.

Instead of passing all parameters to a main function (which is complicated for the user since the dimensions of some of the parameters depend on themselves, e.g. if n=2, vec_n is length 2), I wanted an internal PARAMETERS object within the package, which all functions could access, and the users can change.

I made a package Test with two functions and an internal list INTERNAL=list(a=2) which is saved in sysdata.rda.

test_function<-function(b){
  INTERNAL$a = b
  print(INTERNAL)
  second_function()
}

second_function<-function(){
  print(INTERNAL$a)
}

However on loading the package, and running it I get the following output:

> test_function(5)
$a
[1] 5

[1] 2

Clearly, the object itself doesn't change outside the function.

I'd appreciate any help / advice in getting this to work.

Upvotes: 0

Views: 190

Answers (1)

user2554330
user2554330

Reputation: 44927

INTERNAL$a = b creates a local copy of INTERNAL in your function, and modifies that. Since you want to modify the global copy, you could use

INTERNAL$a <<- b

but this is a bad idea, and probably wouldn't work in a package: you can't modify most values in a package after it is installed.

Alternatives to this are to make INTERNAL into an environment (which you can modify), or create a function that returns the values you want, e.g.

    INTERNAL <- function(a = "default", b = "default") {
      list(a = a, b = b)
    }

    INTERNAL(a = 2)
#> $a
#> [1] 2
#> 
#> $b
#> [1] "default"

Created on 2021-04-19 by the reprex package (v1.0.0)

You can combine these two ideas:

INTERNAL <- local({
    saved <- list(a = "default", b = "default")
    function(...) {
      saved <<- modifyList(saved, list(...))
      saved
    }
})
INTERNAL(a = 1)
#> $a
#> [1] 1
#> 
#> $b
#> [1] "default"
INTERNAL(b = 2)
#> $a
#> [1] 1
#> 
#> $b
#> [1] 2
INTERNAL(c = 3)
#> $a
#> [1] 1
#> 
#> $b
#> [1] 2
#> 
#> $c
#> [1] 3

Created on 2021-04-19 by the reprex package (v1.0.0)

Upvotes: 1

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