R help - Aug 2005 - oldClass vs. class

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.

Anynone can help me ?


2005-08-06

------
Deparment of Sociology
Fudan University

Blog:http://sociology.yculblog.com

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