10  A Simple Function

10.1 Function structure

• All R functions have three parts:
• the body(), the code inside the function.
• the formals(), the list of arguments which controls how you can call the function.
• the environment(), the map of the location of the function’s variables.

10.2 A simple function structure

• Function assignment
• Function assignment with and without ()
• Function outputs
• Function with return
• Function with mandatory and default arguments

Code

fn_mean = function(x) {
    xn = length(x)
    xsum = sum(x)
    xmean = xsum/xn
    return(xmean)
}

10.3 Data

Code

A = c(11, 12, 15, 14, 18)

B = c(NA, 12, 15, 14, 18)

10.4 Class

Code

class(fn_mean)

[1] "function"

10.5 Function argument

Code

formals(fn_mean)

$x

10.6 Function body

Code

body(fn_mean)

{
    xn = length(x)
    xsum = sum(x)
    xmean = xsum/xn
    return(xmean)
}

10.7 Function environment

Code

environment(fn_mean)

<environment: R_GlobalEnv>

10.8 Call a function

Code

fn_mean(A)

[1] 14

10.9 Assign a function outcome

Code

A_mean = fn_mean(A)

A_mean

[1] 14

10.10 Another call

Code

fn_mean(B)

[1] NA

10.11 Function structure

Code

import numpy as np

def fn_mean(x): 
  xn = len(x) 
  xsum = np.sum(x) 
  xmean = xsum / xn 
  return xmean

A = [11, 12, 15, 14, 18]

fn_mean(A)