All valid values of an argument of a function in R

Question

Suppose we have an R function whose arguments must be selected out of a finite set of elements. Like `qplot(..., geom="")`. And `geom` can take only some values, like `bar` or `point`. How can I find out all the valid values the argument of a given function may take? Apart from docs or Internet, which often miss all possible values. Perhaps, some R function can help?

Accepted Answer

If the function of interest is defined like

```
f <- function(a = c("foo","bar")) {
    match.arg(a)
}
```

i.e. when the options are defined as a vector to be later checked with `match.arg` function, then you could use the `formals` function which would give you a list of arguments with the values like in the following example

```
> formals(f)
$a
c("foo", "bar")
```

Otherwise I don't think it is possible to get all valid argument values without RTFSing.

All valid values of an argument of a function in R

Solution

Problem