Two R questions:
typeof
) and the class (returned by class
) of a variable? Is the difference similar to that in, say, C++ language?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.