[R] Optional variables in function?

[Joerg van den Hoff]

jim holtman wrote:
> ?missing
> 
> On 7/2/06, Jonathan Greenberg <jgreenberg at arc.nasa.gov> wrote:
>> I'm a bit new to writing R functions and I was wondering what the "best
>> practice" for having optional variables in a function is, and how to test
>> for optional and non-optional variables?  e.g. if I have the following
>> function:
>>
>> helpme <- function(a,b,c) {
>>
>>
>> }
>>
>> In this example, I want c to be an optional variable, but a and b to be
>> required.  How do I:
>> 1) test to see if the user has inputted c
>> 2) break out of the function of the user has NOT inputted a or b.

if(missing(c))
    stop("need c")

or

if(missing(c))
    return()

depending on your problem it might be better to provide sensible default 
values for a,b,c in the function definition

helpme<-function(a=A, b=B, c=C) {...}

instead of enforcing that every argument is specified?

joerg


>>
>> Thanks!
>>
>> --j
>>
>> --
>>
>> Jonathan A. Greenberg, PhD
>> NRC Research Associate
>> NASA Ames Research Center
>> MS 242-4
>> Moffett Field, CA 94035-1000
>> Phone: 415-794-5043
>> AIM: jgrn3007
>> MSN: jgrn3007 at hotmail.com
>>
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> 
> 
>