On Tue, 10 Jun 2008, John Chambers wrote:
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.)
Not compelling, but there are more hoops to jump through, and hence more
to fail (as here). One point that is a little more serious is that show()
is in methods, and with S3 objects it might be the case that the methods
package is not loaded and hence show() is not visible.
For completeness, I should point out that you can define S4 methods for
print() and S4 methods for show() for S3 classes. If you do that, things
may not work consistently (not least because you will have an S4 generic
'print' that may not be found in preference to base::print), but we do
discourage it.
I find it is rarely needed to call print() or show() explicitly, and when
I do I follow the same rule as auto-printing - use show() when I know I
have an S4 object and print() otherwise.
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
______________________________________________
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
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
