If we need to perform some computation that isn't already a function in R a multiple number of times, we usually do so by defining our own functions. A custom function in R is defined using the following syntax:

> function.name <- function(argument1, argument2, ...){ + # some functionality + }

For example, if we wanted to write a function that determined if a number supplied as an argument was `even`, we can do so in the following manner:

> is.even <- function(a.number){ + remainder <- a.number %% 2 + if(remainder==0) + return(TRUE) + return(FALSE) + } > # testing it > is.even(10)[1] TRUE> is.even(9)[1] FALSE

As an example of a function that takes more than one argument, let's generalize the preceding function by creating a ...