CODEWITHSUNDEEP
r
user399470
user399470

Reputation:

Get a list of all function parameters from inside the function

Is there a way to get all function parameters from within a function?

match.call() doesn't return parameters with defaults set but not overridden. For example:

xf <- function (a, b="Hi", c=TRUE) {
  print(as.list(match.call(expand.dots=FALSE)))
}

>xf(3)
[[1]]
xf

$a
[1] 3

I am writing a package with a function that calls an existing function, but I want to be able to set defaults that are not on the existing function. (I was planning on using the list from match.call, passing it into the other function with do.call and returning the result.

Update: An interesting issue that relates to S3 methods. I created a new S3 method, and used @Ferdinand.kraft's answer. as.list(environment(), all.names=TRUE) The all.names argument keeps names starting with a . in the list. It turns out the the method dispatch adds several arguments to the function environment, including .Generic .Class .Method and several others. This could cause problems if you pass these on to the function in do.call. One of the other answers may be a better all around solution, but I like the simplicity of as.list(environment()).

Upvotes: 10

Views: 2669

Answers (2)

Ferdinand.kraft
Ferdinand.kraft

Reputation: 12829

You can also return the environment at the beginning of the function:

xf <- function (a, b="Hi", c=TRUE) {
  as.list(environment(), all=TRUE)
}

Result:

> xf(a=1)
$a
[1] 1

$b
[1] "Hi"

$c
[1] TRUE

Upvotes: 11

mnel
mnel

Reputation: 115485

You can use ls and mget. ls will (by default), list the objects in the calling frame (in this case, within the function), mget will get these.

eg

xf <- function(a,b='Hi',c){
  # this gets the current definitions of `a`, `b`, and `c` 
  incall <-mget(ls())
  incall}

 xf(3)
## $a
## [1] 3
## 
## $b
## [1] "Hi"
##
## $c

You can then use do.call(whatever, incall)

Upvotes: 6

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