List of all possible classes of R objects

Question

Assuming a fresh R installation, a clean .Rprofile, no additional packages loaded, and no previous calls of the kind class(x) <- "new.class": What are the possible return values of class(x)?

Answer 1

Possible values of class in R

The question is: What are the possible values class can take in R? In R, users can define their own classes (as many as you want). Try creating a class for object x using class(x) <- "new.class". But, at a clean install, R starts with this list of basic classes.

Inspect the class of an object using class().

Atomic classes

Classes help describe the type of data contained in a vector. Coercion (changing classes) moving up the subsequent list is safe—it will preserve information. But changing class downward may lose information.

• character c("hello", "world")
• complex c(as.complex(-1), 2i)
• numeric c(as.integer(10), 3L)
• integer c(100, .5)
• logical c(TRUE, FALSE)

Other common classes

Classes also help describe the logical structure of the data. (Note: type is the physical structure of the data, and sometimes the class is the same as the type thanks to inheritance.)

• atomic vectors: class(my.atomic.vector) will return one of the value from the list above, all elements are homogenous
• matrix: a vector with special 2-dimension attributes
• array: a vector with special n-dimension attributes
• list: elements can be from heterogeneous classes
• data frame: a list with special properties

Answer 2

Find defined classes in R

I had the same question and to me a the best way to find out the defined classes was to simply type in is. and see what appears in the autocompletion menu. Like this:

As you can see you get a list which even considers the loaded packages. Here I have ggplot2 loaded and the corresponding classes are shown in the menu, too.