Add string of (variable number of) arguments to a function within a function

Question

Let's say I have a function that creates x number of objects based on the length of an input variable. I then want those x number of objects to be used as arguments in a function I supply to my function. Assumign that my number of arguments is variable (based on the number of argument names provided), how can I do this?

Can I do this via a string of argument names perhaps?

A non-working example to illustrate what I'm asking:

(in this case, using arguments created outside the function to simplify the example):

foo <- 1:5
na.rm <- T
func <- mean

f1 <- function(func,arg.names) { 
  func(get(arg.names)) }
f1(func,arg.names = c('foo','na.rm')

How do I do this in a way that get's all arguments from my list?

akrun · Accepted Answer · 2017-01-05 03:13:33Z

2

We can try with mget

f1 <- function(func,arg.names) { 
      lst <- mget(arg.names, envir = parent.frame())
        func(lst[[1]], na.rm = lst[[2]])
 }

f1(func, arg.names = c('foo', 'na.rm'))
#[1] 3

Or another option is do.call (as mentioned in the @thelatemail's post) but change the name of the first list element to 'x' as x is the 'data' argument in the mean function

## Default S3 method:

mean(x, trim = 0, na.rm = FALSE, ...)

 f1 <- function(func,arg.names) { 
        lst <- mget(arg.names, envir = parent.frame())
        names(lst)[1] <- 'x'
         do.call(func, lst)
     }

f1(func, arg.names = c('foo', 'na.rm'))
#[1] 3

edited Jan 5, 2017 at 3:13

answered Jan 5, 2017 at 3:07

akrun

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2 Comments

theforestecologist Over a year ago

Perfect! This is exactly what I'm looking for! Thanks @akrun. But now the real question...is this the right (best) way to accomplish what I'm trying to do?? Or is my approach perhaps a "sloppy" or inappropriate approach?

akrun Over a year ago

@theforestecologist THanks, Regarding the question, it depends on why you have to go through this route. Perhaps you can post a new question giving more details about the final objective.

thelatemail · Accepted Answer · 2017-01-05 03:07:16Z

1

The magic of ?do.call awaits you:

do.call(func, list(foo, na.rm=na.rm))
#[1] 3

This essentially just creates and runs:

func(foo, na.rm=na.rm)

...where the arguments to func are passed in as a (potentially named) list.

answered Jan 5, 2017 at 3:07

thelatemail

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2 Comments

theforestecologist Over a year ago

what if I have to supply arguments as strings, vs the object names themselves? (e.g., 'foo' & 'na.rm' vs. foo & na.rm)

thelatemail Over a year ago

@theforestecologist - I think akrun has you covered below.

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