[R] coping with a warning in if()

[Lyman, Mark]

Héctor Villalobos <hvillalo <at> ipn.mx> writes:

> 
> Hi,
> 
> I'm sure this one is very easy....
> 
> I am trying to write a function where one of its arguments has two posible (strings) values, 
> defaulting to one of them if none is specified. My problem is that when evaluating the function 
> the following warning is produced:
> 
> "the condition has length > 1 and only the first element will be used"
> 
> I've read the help page of if() but I don't get it because when evaluating step by step the 
> warning is not produced.
> 
> Omitting the details of my function, below is an example of this 
> 
> ## Function
> fun <- function( n, result = c("simple", "complete") )
> {
>   if ( is.null(result) ) 
>      result <-  "simple" 
>   if ( !(result %in% c("simple", "s", "complete", "c")) ) {
>       stop("specify type of result 'simple' or 'complete'")
>  } else {
>   res <- rnorm(n)
>   res
>  }
> }

Take a look at ?match.arg for one solution.

fun <- function( n, result = c("simple", "complete") )
{
  result <- match.arg(result)
  res <- rnorm(n)
  res

}

fun(n=20)
fun(n=20, result="simple")
fun(n=20, result="comp")
fun(n=20, result="something")

Mark Lyman