R 如何解释is（）的输出？

当我在单个变量上调用

is

函数时，我得到了以下信息

> is(a)
[1] "integer"             "double"              "numeric"            
[4] "vector"              "data.frameRowLabels"

ex <- extends("integer", fullInfo=TRUE)
str(ex)
# List of 5
# $ double             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "double"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi FALSE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ numeric            :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "numeric"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ vector             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "vector"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ data.frameRowLabels:Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "data.frameRowLabels"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ integer            : logi TRUE

这些信息告诉我们什么？为什么我们有三个不同的属性，例如[1]中的整数、双精度和数字

那么

data.frameRowLabel

在这里意味着什么呢？

调用

is（object，class2）

而不使用第二个参数，我们可以得到对象（第一个元素）的

类以及扩展（以下元素）

检查
is（a）
的其他类的定义可以发现
“integer”
是它们的一个子类

selectSuperClasses("integer")  ## don't know why `"double"` isn't listed there...!
# [1] "numeric"             "vector"              "data.frameRowLabels"

getClassDef("data.frameRowLabels")
# Extended class definition ( "ClassUnionRepresentation" )
# Virtual Class "data.frameRowLabels" [package "methods"]
# 
# No Slots, prototype of class "character"
# 
# Known Subclasses: 
# Class "character", directly
# Class "integer", directly
# Class "signature", by class "character", distance 2
# Class "className", by class "character", distance 2
# Class "ObjectsWithPackage", by class "character", distance 2
# Class "factor", by class "integer", distance 2
# Class "ordered", by class "integer", distance 3

## also try:
getClassDef("numeric")
getClassDef("vector")
getClassDef("double")  ## lists `"integer"` as subclass

我们可以检查对象是否扩展到特定的类

is(a, "integer")
# [1] TRUE

is(a, "Date")
# [1] FALSE

## compare    
is(Sys.Date(), "Date")
# [1] TRUE

扩展和模式是不同的东西：

is(a, "double")
# [1] TRUE

## but
is.double(a)  ## tests the mode not the class resp. extend!
# [1] FALSE

为了测试对象和类之间的继承关系，我们可以使用
扩展（class1，class2，maybe=TRUE，fullInfo=FALSE）
：

使用
fullInfo=TRUE
给出所有
is
-关系的完整定义。有关更多信息，请参阅

> is(a)
[1] "integer"             "double"              "numeric"            
[4] "vector"              "data.frameRowLabels"

ex <- extends("integer", fullInfo=TRUE)
str(ex)
# List of 5
# $ double             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "double"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi FALSE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ numeric            :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "numeric"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ vector             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "vector"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ data.frameRowLabels:Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "data.frameRowLabels"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ integer            : logi TRUE

ex运行
a
时返回的内容？如果您包含一个简单的示例输入和所需的输出，可用于测试和验证可能的解决方案，则会更容易为您提供帮助。您试图通过调用此函数来实现什么？可以使用
is（1L）
extends("integer")
# [1] "integer"             "double"              "numeric"            
# [4] "vector"              "data.frameRowLabels"

ex <- extends("integer", fullInfo=TRUE)
str(ex)
# List of 5
# $ double             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "double"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi FALSE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ numeric            :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "numeric"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ vector             :Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "vector"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ data.frameRowLabels:Formal class 'SClassExtension' [package "methods"] with 10 slots
# .. ..@ subClass  : chr "integer"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ superClass: chr "data.frameRowLabels"
# .. .. ..- attr(*, "package")= chr "methods"
# .. ..@ package   : chr "methods"
# .. ..@ coerce    :function (from, strict = TRUE)  
#   .. ..@ test      :function (object)  
#     .. ..@ replace   :function (from, to, value)  
#       .. ..@ simple    : logi TRUE
# .. ..@ by        : chr(0) 
# .. ..@ dataPart  : logi FALSE
# .. ..@ distance  : num 1
# $ integer            : logi TRUE