[R] Argument validation within functions

[Uwe Ligges]

On 06.12.2011 13:46, Johannes Radinger 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?

Yes, see:
?"!"

Uwe Ligges


> 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.
>
> --
>
> ______________________________________________
> 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.