The function show() is intended as a mechanism for automatic display of
objects, a vehicle for writing methods that control the automatic
display of new classes of objects (as noted in its documentation and in
"Programming with Data").
That's why, unlike print() or plot(), it has no optional arguments to
control its behavior.
That said, it was always intended to call print() for S3 objects, as
would be obvious from reading the code for showDefault(). It's just a
glitch that it doesn't, as Brian inferred. We'll fix it, and your usage
should then be perfectly OK. (The relevance of efficiency when one is
printing objects for humans to look at is not compelling.)
John
Laurent Gautier wrote:
> 2008/6/10 Prof Brian Ripley <[EMAIL PROTECTED]>:
>
>> On Tue, 10 Jun 2008, Laurent Gautier wrote:
>>
>>
>>> 2008/6/10 Prof Brian Ripley <[EMAIL PROTECTED]>:
>>>
>>>> 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.
>>
>
> Fair enough.
> May be that word of caution could appear in the documentation for "show" then
> ?
>
> A good place could be where the documentation says:
> The 'methods' package overrides the base definition of
> 'print.default' to arrange for automatic printing to honor methods
> for the function 'show'.
>
> which led me to think that "show" is covering more cases than "print" does
> (while apparently the opposite is happening with "print" delegating to
> "show").
>
>
>
> Thanks,
>
>
>
> 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@r-project.org mailing list
>>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>>>
>>>>>
>>>> --
>>>> Brian D. Ripley, [EMAIL PROTECTED]
>>>> 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, [EMAIL PROTECTED]
>> 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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> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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