[R] oldClass vs. class

[Prof Brian Ripley]

On Sat, 6 Aug 2005, ronggui wrote:

> Hi,When I read the source of str,i find  these code
> -----
>  ## Show further classes // Assume that they do NOT have an own Method --
>    ## not quite perfect ! (.Class = 'remaining classes', starting with current)
>    cl <- oldClass(object); cl <- cl[cl != "data.frame"] #- not THIS 
> class -----

> so I use ?oldClass to try to learn more about oldClass.But 
> after I have reading all the help page ,I still have no idea the 
> diiference between oldClass and class.

>From the help page

      Many R objects have a 'class' attribute, a character vector giving
      the names of the classes which the object "inherits" from.  If the
      object does not have a class attribute, it has an implicit class,
      '"matrix"', '"array"' or the result of 'mode(x)'.  (Functions
      'oldClass' and 'oldClass<-' get and set the attribute, which can
      also be done directly.)

so class returns the implicit class, and oldClass does not.

> A <- matrix(1:6, 2,3)
> class(A)
[1] "matrix"
> oldClass(A)
NULL

just as it says.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595