Writing Functions

Intermediate R

Filip Schouwenaars

DataCamp Instructor

When write your own?

• Solve a particular, well-defined problem
• Black box principle
• If it works, inner workings less important

The triple() function

The triple() function

my_fun <- function(arg1, arg2) {
  body
}

The triple() function

triple <- function(arg1, arg2) {
  body
}

The triple() function

triple <- function(x) {
  body
}

The triple() function

triple <- function(x) {
  3 * x
}

The triple() function

triple <- function(x) {
  3 * x
}

ls()

"triple"

triple(6)

18

• Numeric 6 matched to argument x (by pos)
• Function body is executed: 3 * 6
• Last expression = return value

return()

triple <- function(x) {
  y <- 3 * x
  return(y)
}

triple(6)

18

The math_magic() function

The math_magic() function

The math_magic() function

The math_magic() function

my_fun <- function(arg1, arg2) {
  body
}

The math_magic() function

math_magic <- function(arg1, arg2) {
  body
}

The math_magic() function

math_magic <- function(a, b) {
  body
}

The math_magic() function

math_magic <- function(a, b) {
  a*b + a/b
}

math_magic(4, 2)

10

math_magic(4)

Error: argument "b" is missing, with no default

Optional argument

math_magic <- function(a, b = 1) {
  a*b + a/b
}

math_magic(4)

8

math_magic(4, 0)

Inf

Use return()

math_magic <- function(a, b = 1) {
  if(b == 0){
    return(0)
  }
  a*b + a/b
}

math_magic(4, 0)

0

Let's practice!

Intermediate R