Learning R

Appendix A. Properties of Variables

R has four different functions that tell you the type of a variable, namely class, typeof, mode, and storage.mode. For some variable types they all give the same answer, but for others they differ, and it gets a little bit complicated.

For the vast majority of code you write, you’ll only ever care about the class. The only time class can’t help you is when you are examining matrices or arrays, and you care about whether the variable contains numbers or characters (or some other type). In this case, you can use one of the other three type functions, or call one of the is.* functions (is.numeric, for example).

Table A-1 shows the values returned by class, typeof, mode, and storage.mode for various variable types.

Table A-1. Comparison of variable class, type, mode, and storage mode

	class	typeof	mode	storage.mode
Logical	logical	logical	logical	logical
Integer	integer	integer	numeric	integer
Floating Point	numeric	double	numeric	double
Complex	complex	complex	complex	complex
String	character	character	character	character
Raw byte	raw	raw	raw	raw
Categorical	factor	integer	numeric	integer
Null	NULL	NULL	NULL	NULL
Logical Matrix	matrix	logical	logical	logical
Numeric Matrix	matrix	double	numeric	double
Character Matrix	matrix	character	character	character
Logical Array	array	logical	logical	logical
Numeric Array	array	double	numeric	double
Character Array	array	character	character	character
List	list	list	list	list
Data Frame	data.frame	list	list	list
Function	function	closure	function	function
Environment	environment	environment	environment ...