Test If an Argument of a Function Is Set or Not in R

Test if an argument of a function is set or not in R

You use the function missing() for that.

f <- function(p1, p2) {
    if(missing(p2)) {
        p2=p1^2
    }
    p1-p2
}

Alternatively, you can set the value of p2 to NULL by default. I sometimes prefer that solution, as it allows for passing arguments to nested functions.

f <- function(p1, p2=NULL) {
    if(is.null(p2)) {
        p2=p1^2
    }
    p1-p2
}

f.wrapper <-function(p1,p2=NULL){
    p1 <- 2*p1
    f(p1,p2)
}
> f.wrapper(1)
[1] -2
> f.wrapper(1,3)
[1] -1

EDIT: you could do this technically with missing() as well, but then you would have to include a missing() statement in f.wrapper as well.

Is there R code to test if variable is a function

You can use is.function to check if some object is a function, for example:

is.function(mean) or is.function(`[[`) would return TRUE, also on a side note there is another function is.primitive which tests for builtins and specials, but in your case you probably would want is.function

In your case :

myfun <- function(fun){
              if(is.function(fun)){
                 return(fun(1))
              } else {
                 warning("You are not passing fun as function")
              }
          }

Testing using:

fun <- function(x)x+2 

would yield 3, but fun <- 1 it would give you warning for calls on myfun(fun)

check Argument in a function r

If I understand you right, you probably want this:

lm.IV2 <- function(endogen, IV=NULL, exogen, df) {
  if (! is.null(IV)) {
    ...
  } 
  else {
    ...
  }
}

Simple syntax question regarding f. in R

The dot at the end has no effect on the syntax, it's just like any other legal character in an identifier. A dot at the beginning has very little effect, but it does mean ls() won't display the variable by default.

In the examples you posted, the author probably used f. to remind the reader that the default value was f, and g. reminds the reader of g.

Partial argument matching means that a user could write test(g = somefn) and R would treat somefn as the value of the g. argument.

In the referenced question where you saw this code, the original function had header

g <- function(x, T, f=f) {

This won't work, because the default value has the same name as the argument, and defaults are evaluated in the frame of the function. So it says "If the argument f is not specified, set it to the argument f." That makes no sense. The corrected version that you posted says "If the argument f. is not specified, set it to the global variable f."

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