[R] Argument validation within functions

[R. Michael Weylandt]

Use the ! (not) operator.

Not sure what you mean by " as the stop() stops the total function":
try the following

f <- function(a){
   stopifnot(a > 3)
   return(a^2)
}

f(2)
f(4)

Michael

(PS -- It's usually asked to cc the list so that this all gets
threaded properly in folks' mailboxes)

On Tue, Dec 6, 2011 at 7:46 AM, Johannes Radinger <JRadinger at gmx.at> wrote:
> Hi,
>
> thank you... I think I will go for the if-stop approach
> as the stop() stops the total function... So there is just
> one little other question: What is the opposite of is.numeric?
> Is ther isnot.numeric? How  can that be implemented in following
> function:
>
> f <- function(a){
>        if(is.numeric(a)) stop("a is not numeric")
>        if(0 > a && a > 1) stop("a must be a value between 0 and 1")
>        a
> }
>
> /Johannes
>
> -------- Original-Nachricht --------
>> Datum: Tue, 6 Dec 2011 07:04:59 -0500
>> Von: "R. Michael Weylandt" <michael.weylandt at gmail.com>
>> An: Johannes Radinger <JRadinger at gmx.at>
>> CC: r-help at r-project.org
>> Betreff: Re: [R] Argument validation within functions
>
>> The quick and dirty way to do so is to use: stopifnot() in conjunction
>> (if necessary with all() and any()). You can replace that first
>> condition with a simple is.numeric() as well. A more helpful way (if
>> this is production code) is to use if statement with the stop()
>> function directly which lets you provide specific error messages.
>>
>> Michael
>>
>> On Tue, Dec 6, 2011 at 6:41 AM, Johannes Radinger <JRadinger at gmx.at>
>> wrote:
>> > Hi,
>> >
>> > I just started with writing functions in R and so some questions popped
>> up.
>> > I provide some values as argument to my function such as:
>> >
>> > function(a,b,c){}
>> >
>> > Now i want that the function first checks if the arguments are valid for
>> the function. E.g argument "a" has to be a number in the range 0-1. How
>> can that easily done?
>> >
>> > So far I have:
>> >
>> >        a <- as.numeric(a)
>> >        if(0 <= a && a <= 1)
>> >
>> > to first check if a is a number...if not the function stops and gives an
>> error message. If it is a number it just continues...
>> >
>> > But how to check the range?
>> > Above there is the if-approach but then the rest of the function is
>> exectued as part of if (or else). Is there a simpler way without having the
>> if-brackets around the remaining code?
>> > Just a check if the value is between 0 and 1 and if yes continue with
>> the next line if no abort the function with a error message? How can such an
>> error message be created?
>> >
>> > thank you and best regards,
>> >
>> > /Johannes
>> > --
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>
> --
> NEU: FreePhone - 0ct/min Handyspartarif mit Geld-zurück-Garantie!
> Jetzt informieren: http://www.gmx.net/de/go/freephone