Building package functions

Developing R Packages

Jasmin Ludolf

Content Developer

R package structure

Example package structure

Different temperature scales

What is 35 degrees Celsius (C) in Fahrenheit (F)?

Confused on the beach

Converting using R

C_value <- 35
F <- 9/5 * C_value + 32
F

[1] 95

Refresher on R functions

temp_converter <- function(

      value,
      unit_from = "Celsius",
      unit_to = "Fahrenheit") {

    if (unit_from == "Celsius" && unit_to == "Fahrenheit") {
    return(value * 9/5 + 32)

    } else if (unit_from == "Fahrenheit" && unit_to == "Celsius") {
    return((value - 32) * 5/9)

    } else if (unit_from == unit_to) {
    warning("unit_from and unit_to are the same, value returned.")
    return(value)

    } else {
    stop("Invalid unit_from or unit_to. Only 'Celsius' and 'Fahrenheit' are accepted.")
    }
 }

Using temp_converter()

temp_converter(100)

[1] 212

temp_converter(95, unit_from = "Fahrenheit", unit_to = "Celsius")

[1] 35

Some R function best practices

Choose descriptive names
Handle all inputs gracefully
Focus on one thing

Store a function in a file

dump("temp_converter", 
     file = "R/temp_converter.R")

Current unitConverter package structure

Install the package with devtools

devtools::install()

-  checking for file 'DESCRIPTION' ...
-  preparing 'unitConverter':
-  checking DESCRIPTION meta-information ...
  --install-tests 
* installing to library
* installing *source* package 'unitConverter' ...
** R
** data
** inst
** testing if installed package can be loaded from temporary location
** testing if installed package can be loaded from final location
* DONE (unitConverter)

Call temp_converter() temperature_data

value	unit
36.26	Celsius

library(unitConverter)

unitConverter:::temp_converter(

    value = temperature_data$value[1],
    unit_from = temperature_data$unit[1],
    unit_to = "Fahrenheit")

[1] 97.268

Let's practice!

Developing R Packages