Check the class of an object
Hi Herv?, thank you very much for your reply! This makes the different treatment of S3 and S4 objects by 'class' clear. Best Simon
On Jul 23, 2013, at 7:20 PM, Herv? Pag?s <hpages at fhcrc.org> wrote:
Hi, 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.
Unlike with S3 objects, class() on an S4 object can only return 1 class. Also note that, on an S3 object, doing "firstClass" %in% class(myObject) is equivalent to doing inherits(myObject, "firstClass"), which is what you said you wanted to avoid. The most specific class should be the first so if that's what you wanted to check, you could do class(myObject)[1] == "firstClass" But that precaution is not needed if 'myObject' is guaranteed to be an S4 object (although when writing a unit test, one should probably discard any guarantee of that sort). Cheers, H.
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]]
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