[R] Help with objects

Duncan Murdoch murdoch.duncan at gmail.com
Mon Apr 25 20:20:47 CEST 2011

Russ Abbott wrote:
> Hi all,
> I would appreciate some help in understanding how to find out about objects.
> For example, to the extent that I understand R it seems to treat everything
> as an object even without declaring them as objects.

That's correct.

  Everything has
> attributes, for example, which are like instance variables in objects.

That's not quite true.  There are a few special kinds of objects which 
can't have attributes.  The NULL object is the only one you're likely to 
meet in regular code.

> addition, there are S3 and S3 category objects.  Is there a good
> introductory description of how these are different from standard R objects
> and how they are different from each other?

S3 and S4 are layers put on top of the regular system for handling 
objects.  S3 objects just have a class attribute, which causes some 
functions to handle them specially; this is introduced in An 
Introduction to R, and more fully described in the R Language 
Definition.  S4 is a more complex system, partly described in the 
?Methods help topic, more completely in the references listed on that page.

Duncan Murdoch

> Also, how does one find out more about how objects are declared. For
> example, Data Mining with
> R<http://www.liaad.up.pt/~ltorgo/DataMiningWithR/code3.html>uses the
> quantmod package. I am used to Java's JavaDoc where one can see how
> classes are declared, what the instance variables and methods are, etc. I
> don't see anything similar for this package.  How, for example, would one
> find out what the instance variables are in a quantmod object and what the
> methods are that are defined on quantmod objects? I know that there is the
> standard quantmod documentation, but that doesn't seem
> to distinguish between standard functions and class-based methods. Nor, as
> far as I can see, does it describe the instance variables in a quantmod
> object.
> Thanks.
> *-- Russ Abbott*
> *_____________________________________________*
> ***  Professor, Computer Science*
> *  California State University, Los Angeles*
> *  Google voice: 747-*999-5105
> *  blog: *http://russabbott.blogspot.com/
>   vita:  http://sites.google.com/site/russabbott/
> *_____________________________________________*
> 	[[alternative HTML version deleted]]
> ______________________________________________
> 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.

More information about the R-help mailing list