Passing the same argument to multiple nested function

Question

I would like to pass the same argument to several nested functions. For example, given 2 functions:

 fun1 = function(x){x^2}
 fun2 = function(x,FUN,...) { x + FUN(...) }

I would like to implement something like this:

 fun2(x=10,FUN=fun1)  ## this returns error

In this example, I would like to get an output of 10 + 10^2 = 110

I have seen this answered question: Passing arbitrary arguments to multiple nested functions in R but I specifically wish to pass the same argument to multiple nested functions.

just to be sure, why not a factory function instead? (see adv-r.hadley.nz/function-factories.html) — Pasqui
– Pasqui, Commented Nov 24, 2018 at 22:13

Kamil Bartoń · Accepted Answer · 2018-11-26 00:45:17Z

2

In your example, ... is what follows the FUN argument, i.e. nothing. You could play with sys.call to reuse the arguments, e.g.:

 fun2 <- function(FUN, x, ...) {
     cl <- match.call(expand.dots = TRUE) # unevaluated expression `fun2(x=10,FUN=fun1)`
# Note: sys.call would work only if the arguments were named
     cl[[1]] <- cl$FUN # substitute `fun2`. Now cl is `fun1(x=10,FUN=fun1)`
     cl$FUN <- NULL # remove FUN argument. Now cl is `fun1(x=10)`
     result.of.FUN <- eval.parent(cl) # evaluate the modified expression
     x + result.of.FUN
 }

edited Nov 26, 2018 at 0:45

answered Nov 24, 2018 at 22:50

Kamil Bartoń

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Comments

jay.sf · Accepted Answer · 2018-11-24 22:16:03Z

1

The xs are not the same in both functions.

Consider this:

fun1 <- function(y) y^2 
fun2 <- function(x,FUN) x + FUN(x) 

> fun2(x=10, FUN=fun1)
[1] 110

You see, if you don't pass the argument with FUN(x), fun1() doesn't recognize the x=10.

answered Nov 24, 2018 at 22:16

jay.sf

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1 Comment

Alex Witsil Over a year ago

I like what you're doing here but have 2 comments. (i) defining fun1 in terms of x (i.e. fun1 <- function(x) {x^2}) will return the correct result and (ii) I am looking for a more general answer. The way you define fun2 indicates that the input function (FUN) will always depend on x, which isn't necessarily true. It would be nice to have a solution where the input function (FUN) doesn't need to have its inputs defined explicitly.

Alex Witsil · Accepted Answer · 2018-11-27 21:00:07Z

0

Another somewhat less robust but perhaps simpler solution as compared Kamil's, is to rely on the argument order of the defined functions as such:

fun1 = function(x){x^2}
fun2 = function(x,FUN,...) { x + FUN(...) }

Then running fun2 as:

 > fun2(x=10,FUN=fun1,10)
 [1] 110

This again relies on knowing the order of the function arguments, which is somewhat dangerous.

answered Nov 27, 2018 at 21:00

Alex Witsil

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