4  Writing Your Own Functions

Sometimes we need to create our own functions for a specific purpose. They are called user-defined functions.

4.1 Syntax

Functions are created using the function()

Main components of a function

  • Function name

  • Function inputs

  • Function body

  • Function output


name <- function(arg1, aug2, ...){

<FUNCTION BODY>

return(value) 

}

Example

cal_power <- function(x){

a <- x^2; b <- x^3
out <- c(a, b)
names(out) <- c("squared", "cubed")
out # or return(out)

}

In this case

  • Function name: cal_power

  • Function inputs: x

  • Function body:

a <- x^2; b <- x^3
out <- c(a, b)
names(out) <- c("squared", "cubed")
  • Function output: out

Evaluation

cal_power(2)
squared   cubed 
      4       8

4.2 Exercise

  1. What are the key factors to consider when selecting a function name in R?

  2. How should function argument names be chosen for clarity and usability?

  3. Is it necessary to explicitly use return() to output a value from a function in R?

4.3 Function with single line

Method 1: with { }

cal_sqrt <- function(x){

x^2

}

Method 2: without { }

cal_sqrt <- function(x) x^2

4.4 Exercise

  1. Write a function to calculate the median.

help:

5%%2
[1] 1
4%%2
[1] 0
  1. Write a function to calculate the correlation coefficient

\[r=\frac{\sum_{i=1}^{n}(x_i-\bar{x})(y_i-\bar{y})}{\sqrt{\sum_{i=1}^n(x_i-\bar{x})^2\sum_{i=1}^n(y_i-\bar{y})^2}}\]