R in a Nutshell, 2nd Edition

Functions

In R, the operations that do all the work are called functions. We’ve already used a few functions above (you can’t do anything interesting in R without them). Functions are just like what you remember from math class. Most functions are in the following form:

f(argument1, argument2, ...)

Where f is the name of the function, and argument1, argument2, . . . are the arguments to the function. Here are a few more examples:

> exp(1)
[1] 2.718282
> cos(3.141593)
[1] -1
> log2(1)
[1] 0

In each of these examples, the functions took only one argument. Many functions require more than one argument. You can specify the arguments by name:

> log(x=64, base=4)
[1] 3

Or, if you give the arguments in the default order, you can omit the names:

> log(64,4)
[1] 3

Not all functions are of the form f(...). Some of them are in the form of operators.^[7] For example, we used the addition operator (“+”) above. Here are a few examples of operators:

> 17 + 2
[1] 19
> 2 ^ 10
[1] 1024
> 3 == 4
[1] FALSE

We’ve seen the first one already: it’s just addition. The second operator is the exponentiation operator, which is interesting because it’s not a commutative operator. The third operator is the equality operator. (Notice that the result returned is FALSE; R has a Boolean data type.)

^[7] When you enter a binary or unary operator into R, the R interpreter will actually translate the operator into a function; there is a function equivalent for each operator. We’ll talk about this more in Chapter 5.