Data Analysis with R, Second Edition - Second Edition

Functions

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 ...