A Comprehensive Survey of the Types of Things in R; 'Mode' and 'Class' and 'Typeof' Are Insufficient

A comprehensive survey of the types of things in R; 'mode' and 'class' and 'typeof' are insufficient

I agree that the type system in R is rather weird. The reason for it being that way is that it has evolved over (a long) time...

Note that you missed one more type-like function, storage.mode, and one more class-like function, oldClass.

So, mode and storage.mode are the old-style types (where storage.mode is more accurate), and typeof is the newer, even more accurate version.

mode(3L)                  # numeric
storage.mode(3L)          # integer
storage.mode(`identical`) # function
storage.mode(`if`)        # function
typeof(`identical`)       # closure
typeof(`if`)              # special

Then class is a whole different story. class is mostly just the class attribute of an object (that's exactly what oldClass returns). But when the class attribute is not set, the class function makes up a class from the object type and the dim attribute.

oldClass(3L) # NULL
class(3L) # integer
class(structure(3L, dim=1)) # array
class(structure(3L, dim=c(1,1))) # matrix
class(list()) # list
class(structure(list(1), dim=1)) # array
class(structure(list(1), dim=c(1,1))) # matrix
class(structure(list(1), dim=1, class='foo')) # foo

Finally, the class can return more than one string, but only if the class attribute is like that. The first string value is then kind of the main class, and the following ones are what it inherits from. The made-up classes are always of length 1.

# Here "A" inherits from "B", which inherits from "C"
class(structure(1, class=LETTERS[1:3])) # "A" "B" "C"

# an ordered factor:
class(ordered(3:1)) # "ordered" "factor"

Types and classes of variables

In R every "object" has a mode and a class. The former represents how an object is stored in memory (numeric, character, list and function) while the later represents its abstract type. For example:

d <- data.frame(V1=c(1,2))
class(d)
# [1] "data.frame"
mode(d)
# [1] "list"
typeof(d)
# list

As you can see data frames are stored in memory as list but they are wrapped into data.frame objects. The latter allows for usage of member functions as well as overloading functions such as print with a custom behavior.

typeof(storage.mode) will usually give the same information as mode but not always. Case in point:

typeof(c(1,2))
# [1] "double"
mode(c(1,2))
# [1] "numeric"

The reasoning behind this can be found here:

The R specific function typeof returns the type of an R object

Function mode gives information about the mode of an object in the sense of Becker, Chambers & Wilks (1988), and is more compatible with other implementations of the S language

The link that I posted above also contains a list of all native R basic types (vectors, lists etc.) and all compound objects (factors and data.frames) as well as some examples of how mode, typeof and class are related for each type.

Ex: Computing a vector of logicals that is true when x[i]0

Long but hopefully easy to understand.

for(i in 1:length(x)){

  if(x[i] > 0){
    y[i] <- TRUE

  } else {
    y[i] <- FALSE
  }
}

How to create a vector of integers with structure()?

try this:

> x <- structure(c(1L,2L))
> is.integer(x)
[1] TRUE

but just

> x <- c(1L,2L)
> is.integer(x)
[1] TRUE

is ok.

Why does class() return not the same inside Map()?

You apply (map) all elements of an empty matrix to a function returning it's class. The class of an empty thing is NA. A vector only containing NAs is of class logical in R.

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