[R] Check the class of an object

[Simon Zehnder]

Hi Martin,

I didn't know that. But that is even more comfortable for checking. Thanks for the quick update!

Best


Simon

P.S. And thanks for the online documents about S4 - I could already learn a lot!


On Jul 23, 2013, at 7:11 PM, Martin Morgan <mtmorgan at fhcrc.org> wrote:

> On 07/23/2013 09:59 AM, Simon Zehnder wrote:
>> Hi David,
>> 
>> thanks for the reply. You are right. Using the %in% is more stable and I gonna change my code.
> 
> you said you were you were using S4 classes. S4 classes do not report vectors of length != 1, from ?class
> 
>     For objects which have a formal class, its name is returned by 'class'
>     as a character vector of length one
> 
> so a first unit test could be
> 
>  stopifnot(length(class(myObject)) != 1L)
> 
> 
>> 
>> When testing for a specific class using 'is' one has to start at the lowest heir and walk up the inheritance structure. Starting at the checks at the root will always give TRUE. Having a structure which is quite complicated let me move to the check I suggested in my first mail.
>> 
>> Best
>> 
>> Simon
>> 
>> On Jul 23, 2013, at 6:15 PM, David Winsemius <dwinsemius at comcast.net> wrote:
>> 
>>> 
>>> On Jul 23, 2013, at 5:36 AM, Simon Zehnder wrote:
>>> 
>>>> Dear R-Users and R-Devels,
>>>> 
>>>> I have large project based on S4 classes. While writing my unit tests I found out, that 'is' cannot test for a specific class, as also inherited classes can be treated as their super classes. I need to do checks for specific classes. What I do right now is sth. like
>>>> 
>>>> if (class(myClass) == "firstClass") {
>>> 
>>> I would think that you would need to use `%in%` instead.
>>> 
>>> if( "firstClass" %in% class(myObject) ){
>>> 
>>> Objects can have more than one class, so testing with "==" would fail in those instances.
>>> 
>>> 
>>>> 
>>>> } else if (class(myClass) == "secondClass") {
>>>> 
>>>> }
>>>> 
>>>> Is this the usual way how classes are checked in R?
>>> 
>>> Well, `inherits` IS the usual way.
>>> 
>>>> I was expecting some specific method (and 'inherits' or 'extends' is not what I look for)...
>>>> 
>>>> 
>>>> Best
>>>> 
>>>> Simon
>>>> 
>>>> 	[[alternative HTML version deleted]]
>>> 
>>> Plain-text format is the recommended format for Rhelp
>>> 
>>> --
>>> David Winsemius
>>> Alameda, CA, USA
>>> 
>> 
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> 
> 
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