r - 测试S4对象是否为实例

如何测试对象是否是S4类的实例(不确定这是否是正确的术语)？我知道函数isS4，但是对于类定义等也返回true。例如:

traj <- setClass(
  Class="Trajectories",
  representation=representation(
    times = "numeric",
    traj = "matrix"
  )
)

trajclass <- getClass("Trajectories")
trajobject <- new(Class="Trajectories",times=c(1,3),traj=matrix(1:4,ncol=2))

isS4(traj)
isS4(trajclass)
isS4(trajobject)

我只对包含数据的对象感兴趣，在这种情况下为trajobject；在方法或类定义上没有那么多。是否可以使用 native 函数测试S4对象是否为实际对象？ IE。当使用print(object)时，输出以以下内容开头:

类“foo”的对象.....

最佳答案

使用S4类(很酷(？)eh？)来定义S4类(以及与此有关的引用类，也许对此有些恼怒)

> class(trajclass)
[1] "classRepresentation"
attr(,"package")
[1] "methods"
> getClass(class(trajclass))
Class "classRepresentation" [package "methods"]

Slots:

Name:             slots         contains          virtual        prototype
Class:             list             list          logical              ANY

Name:          validity           access        className          package
Class: OptionalFunction             list        character        character

Name:        subclasses       versionKey           sealed
Class:             list      externalptr          logical

Known Subclasses: "ClassUnionRepresentation", "refClassRepresentation"

我认为您能做的最好的就是

isS4(trajclass) && !is(trajclass, "classRepresentation")

S4使用show作为print的同义词(一种)；对于show，有一个S4 classRepresentation方法，即

> selectMethod(show, class(traj))
Method Definition:

function (object)
{
    cat(gettextf("Class generator function for class \"%s\" from package \"%s\"\n",
        object@className, object@package))
    show(as(object, "function"))
}
<bytecode: 0x1522d40>
<environment: 0xf1d808>

Signatures:
        object
target  "classGeneratorFunction"
defined "classGeneratorFunction"

而show的trajobject方法是默认方法，即

> selectMethod(show, class(trajobject))
Method Definition (Class "derivedDefaultMethod"):

function (object)
showDefault(object, FALSE)
<bytecode: 0x1516d08>
<environment: namespace:methods>

Signatures:
        object
target  "Trajectories"
defined "ANY"

用methods::showDefault中的肉。我想你可以实现

setGeneric("isNotS4ClassDef",
    function(object) standardGeneric("isNotS4ClassDef"))

setMethod(isNotS4ClassDef, "ANY",
    function(object) TRUE)

setMethod(isNotS4ClassDef, "classRepresentation",
    function(object) FALSE)

关于r - 测试S4对象是否为实例，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/10858807/