show {methods}R Documentation

Show an Object

Description

Display the object, by printing, plotting or whatever suits its class. This function exists to be specialized by methods. The default method calls showDefault.

Formal methods for show will usually be invoked for automatic printing (see the details).

Usage

show(object)

Arguments

object Any R object

Details

The methods package overrides the base definition of print.default to arrange for automatic printing to honor methods for the function show. This does not quite manage to override old-style printing methods, since the automatic printing in the evaluator will look first for the old-style method.

If you have a class myClass and want to define a method for show, all will be well unless there is already a function named print.myClass. In that case, to get your method dispatched for automatic printing, it will have to be a method for print. A slight cheat is to override the function print.myClass yourself, and then call that function also in the method for show with signature "myClass".

Value

show returns an invisible NULL.

See Also

showMethods prints all the methods for one or more functions; showMlist prints individual methods lists; showClass prints class definitions. Neither of the latter two normally needs to be called directly.

Examples

## following the example shown in the setMethod documentation ...
setClass("track",
         representation(x="numeric", y="numeric"))
setClass("trackCurve", 
         representation("track", smooth = "numeric"))

t1 <- new("track", x=1:20, y=(1:20)^2)

tc1 <- new("trackCurve", t1)

setMethod("show", "track",
  function(object)print(rbind(x = object@x, y=object@y))
)
## The method will now be used for automatic printing of t1

t1

## Not run: 
  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
x    1    2    3    4    5    6    7    8    9    10    11    12
y    1    4    9   16   25   36   49   64   81   100   121   144
  [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
x    13    14    15    16    17    18    19    20
y   169   196   225   256   289   324   361   400
## End(Not run)
## and also for tc1, an object of a class that extends "track"
tc1

## Not run: 
  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
x    1    2    3    4    5    6    7    8    9    10    11    12
y    1    4    9   16   25   36   49   64   81   100   121   144
  [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
x    13    14    15    16    17    18    19    20
y   169   196   225   256   289   324   361   400
## End(Not run)

[Package methods version 2.1.0 Index]