Get Object methods R - r

Question

Given an arbitrary R object, how can I obtain all the methods associated with the object?

Answer 1

The closest I can think of is methods (if S3 object/function, List all available methods for an S3 generic function, or all methods for a class.), or showMethods (if S4).
e.g.:
> A <- matrix(runif(10))
> B <- methods(class=class(A))
> B
[1] anyDuplicated.matrix as.data.frame.matrix as.raster.matrix*
[4] boxplot.matrix determinant.matrix duplicated.matrix
[7] edit.matrix* head.matrix isSymmetric.matrix
[10] relist.matrix* subset.matrix summary.matrix
[13] tail.matrix unique.matrix
Non-visible functions are asterisked
> attr(B,'info')
visible from
anyDuplicated.matrix TRUE package:base
as.data.frame.matrix TRUE package:base
as.raster.matrix FALSE registered S3method
boxplot.matrix TRUE package:graphics
determinant.matrix TRUE package:base
duplicated.matrix TRUE package:base
edit.matrix FALSE registered S3method
head.matrix TRUE package:utils
isSymmetric.matrix TRUE package:base
relist.matrix FALSE registered S3method
subset.matrix TRUE package:base
summary.matrix TRUE package:base
tail.matrix TRUE package:utils
unique.matrix TRUE package:base
Or for a function:
> methods(summary)
[1] summary.aov summary.aovlist summary.aspell*
[4] summary.connection summary.data.frame summary.Date
[7] summary.default summary.ecdf* summary.factor
[10] summary.glm summary.infl summary.lm
[13] summary.loess* summary.manova summary.matrix
[16] summary.mlm summary.nls* summary.packageStatus*
[19] summary.PDF_Dictionary* summary.PDF_Stream* summary.POSIXct
[22] summary.POSIXlt summary.ppr* summary.prcomp*
[25] summary.princomp* summary.srcfile summary.srcref
[28] summary.stepfun summary.stl* summary.table
[31] summary.tukeysmooth*
Non-visible functions are asterisked
?Methods may also prove a useful read.

Answer 2

The class of an R object is recovered with class. Objects do not have methods associated with them in typical R parlance. The class of an object determines what function-methods will be applied to it. In order to determine what functions have methods associated with a given class you would need to test all available functions to see whether there was a class-specific method. Even then generic functions would attempt to use a "default" method in most instances.
Some methods associated with a generic S3 function are displayed with methods. The methods of an S4 function are recovered with showMethods. So, for what most people would call "objects", your question does not make sense, but if it happened that you were including functions under the general term "objects" (which is technically fair) then I have answered.
showMethods(classes="data.frame")
methods(class="data.frame")
Then there are a group of methods that might be called "implicit" although their R name is "groupGeneric"
?groupGeneric
methods("Math") # These are "add-on" methods to the primitive Math functions
[1] Math.data.frame Math.Date Math.dates* Math.difftime Math.factor
[6] Math.mChoice Math.polynomial* Math.POSIXt Math.ratetable* Math.Surv*
[11] Math.times*
Non-visible functions are asterisked
?"+"
methods("Ops") # The binary operators such as "+", "-", "/"
[1] Ops.data.frame Ops.Date Ops.dates* Ops.difftime Ops.factor
[6] Ops.findFn Ops.mChoice Ops.numeric_version Ops.ordered Ops.polynomial*
[11] Ops.POSIXt Ops.raster* Ops.ratetable* Ops.Surv* Ops.times*
[16] Ops.ts* Ops.unit* Ops.yearmon* Ops.yearqtr* Ops.zoo*
Non-visible functions are asterisked
And even then you have not really display the members of the Math or the Ops family, but you would have seen them at the help page for ?groupGeneric. You do not see Ops.numeric. A somewhat lower level view is provided by:
.Primitive("+")
# function (e1, e2) .Primitive("+")
These will throw an error if offered the wrong class argument.

Answer 3

Some packages define functions that are not methods but which are nevertheless intended for use with a particular class. For example, library(igraph) defines the function radius(_), which is intended for use on objects in the igraph class. Since such functions are not methods, methods(_) and showMethods(_) will not reveal them.
In such cases, lsf.str(_) can be very helpful. For example:
lsf.str("package:igraph")
includes the line:
radius : function (graph, mode = c("all", "out", "in", "total"))