[Rd] Error in "getClass" when calling the function "show"

[Martin Maechler]

>>>>> "LG" == Laurent Gautier <lgautier at gmail.com>
>>>>>     on Tue, 10 Jun 2008 09:58:17 +0200 writes:

    LG> 2008/6/10 Prof Brian Ripley <ripley at stats.ox.ac.uk>:
    >> On Tue, 10 Jun 2008, Laurent Gautier wrote:
    >> 
    >>> 2008/6/10 Prof Brian Ripley <ripley at stats.ox.ac.uk>:
    >>>> 
    >>>> showDefault has
    >>>> 
    >>>> clDef <- getClass(class(object))
    >>>> 
    >>>> Looks like the showDefault code intended
    >>>> 
    >>>> clDef <- getClass(class(object), .force=TRUE)
    >>>> 
    >>>> However, why are you calling show() on a non-S4 object?
    >>>> I cannot see any advtanges in doing so.
    >>> 
    >>> I'd like *one* printing method for all objects, and the
    >>> generic "show" is registered as working for ANYthing
    >>> (see below) ?
    >> 
    >> print() calls show() for S4 objects (with no additional
    >> arguments).
    >> 
    >> I agree show() ought to do what it is documented to, but
    >> calling it on non-S4 objects is inefficient.

In any case, the buglet that Laurent reported  has now been
fixed in R-patched and R-devel, using  ", .Force = TRUE "
almost as Brian Ripley had proposed.

Martin

    LG> Fair enough.  May be that word of caution could appear
    LG> in the documentation for "show" then ?

    LG> A good place could be where the documentation says: The
    LG> 'methods' package overrides the base definition of
    LG> 'print.default' to arrange for automatic printing to
    LG> honor methods for the function 'show'.

    LG> which led me to think that "show" is covering more cases
    LG> than "print" does (while apparently the opposite is
    LG> happening with "print" delegating to "show").



    LG> Thanks,



    LG> Laurent




    >>> Or is defining one's own function currently recommended
    >>> ?
    >>> 
    >>> myPrint <- function(x, ...)  { if (isS4(x)) { show(x,
    >>> ...)  } else { print(x, ...)  } }
    >>> 
    >>>> showMethods("show")
    >>> 
    >>> Function: show (package methods) object="ANY"
    >>> object="classRepresentation"
    >>> object="derivedDefaultMethod" (inherited from:
    >>> object="MethodDefinition") object="function" (inherited
    >>> from: object="ANY") object="genericFunction"
    >>> object="MethodDefinition" object="MethodsList"
    >>> (inherited from: object="ANY") object="MethodWithNext"
    >>> object="ObjectsWithPackage" object="signature"
    >>> object="traceable"
    >>> 
    >>>> showMethods("print")
    >>> 
    >>> Function "print": <not a generic function>
    >>>> 
    >>>> getMethod("show", "ANY")
    >>> 
    >>> Method Definition (Class "derivedDefaultMethod"):
    >>> 
    >>> function (object) showDefault(object, FALSE)
    >>> <environment: namespace:methods>
    >>> 
    >>> Signatures: object target "ANY" defined "ANY"
    >>> 
    >>> 
    >>>> On Tue, 10 Jun 2008, Laurent Gautier wrote:
    >>>> 
    >>>>> Dear List,
    >>>>> 
    >>>>> Calling "show" on an object of class "summary.lm"
    >>>>> gives: Error in getClass(class(object)) : "summary.lm"
    >>>>> is not a defined class
    >>>>> 
    >>>>> Is this a miss on my end ?
    >>>>> 
    >>>>> 
>>>>> x <- seq(1, 10)
>>>>> show(x)
    >>>>> 
    >>>>> [1] 1 2 3 4 5 6 7 8 9 10
    >>>>>> 
>>>>> y <- runif(10)
>>>>> fit <- lm(y ~ x)
>>>>> show(fit)
    >>>>> 
    >>>>> Call: lm(formula = y ~ x)
    >>>>> 
    >>>>> Coefficients: (Intercept) x 1.04938 -0.08869
    >>>>> 
>>>>> show(summary(fit))
    >>>>> 
    >>>>> Error in getClass(class(object)) : "summary.lm" is not
    >>>>> a defined class
    >>>>>> 
>>>>> class(summary(fit))
    >>>>> 
    >>>>> [1] "summary.lm"
    >>>>>> 
>>>>> class((fit))
    >>>>> 
    >>>>> [1] "lm"
    >>>>>> 
>>>>> getClass("lm")
    >>>>> 
    >>>>> Virtual Class
    >>>>> 
    >>>>> No Slots, prototype of class "S4"
    >>>>> 
    >>>>> Extends: "oldClass"
    >>>>> 
    >>>>> Known Subclasses: Class "mlm", directly Class "aov",
    >>>>> directly Class "glm", directly Class "maov", by class
    >>>>> "mlm", distance 2 Class "glm.null", by class "glm",
    >>>>> distance 2
    >>>>>> 
>>>>> getClass("summary.lm")
    >>>>> 
    >>>>> Error in getClass("summary.lm") : "summary.lm" is not
    >>>>> a defined class
    >>>>>> 
>>>>> sessionInfo()
    >>>>> 
    >>>>> R version 2.7.0 Patched (2008-06-07 r45877)
    >>>>> i686-pc-linux-gnu
    >>>>> 
    >>>>> locale:
    >>>>> 
    >>>>> 
    >>>>> LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=C;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C
    >>>>> 
    >>>>> attached base packages: [1] stats graphics grDevices
    >>>>> utils datasets methods base
    >>>>> 
    >>>>> 
    >>>>> Laurent
    >>>>> 
    >>>>> ______________________________________________
    >>>>> R-devel at r-project.org mailing list
    >>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
    >>>>> 
    >>>> 
>>> --
>>> 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
    >>>> 
    >>> 
>
> --
> 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
    >> 

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