Check the class of an object

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

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David Winsemius
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Check the class of an object

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