Creating the `rhello` R package

Your Name The Date

How I created this repo

I created a new empty repo named rhello-project in GitHub and ran the following from an R console:

rmarkdown::draft("README.Rmd",
                 template = "make-an-r-package",
                 package = "litr")

At the top of README.Rmd, I changed output: litr::litr_html_document to output: github_document.
I pressed “Knit” in RStudio. (Alternatively could have run litr::render("README.Rmd") from the R console.). This generated rhello and README.md. [And of course I then added this section describing what I did!]

Package setup

We start by specifying the information needed in the DESCRIPTION file of the R package.

usethis::create_package(
  path = ".",
  fields = list(
    Package = params$package_name,
    Version = "0.0.0.9000",
    Title = "A Package That Says Hello",
    Description = "This package says hello.  But its actual purpose is to show how an R package can be completely coded in a single R markdown file.",
    `Authors@R` = person(
      given = "First",
      family = "Last",
      email = "you@gmail.com",
      role = c("aut", "cre")
      )
  )
)
usethis::use_mit_license(copyright_holder = "F. Last")

Now to the package itself

Define a function

Let’s define a function for our R package:

#' Say hello to someone
#' 
#' @param name Name of a person
#' @param exclamation Whether to include an exclamation mark
#' @export 
say_hello <- function(name, exclamation = TRUE) {
  paste0("Hello ", name, ifelse(exclamation, "!", "."))
}

Code chunks whose first line starts with #' are added to the package.

We can try running it.

say_hello("Jacob")

## [1] "Hello Jacob!"

That code chunk does not start with #', so it is not added to the package.

Let’s write some tests to make sure the function behaves as desired:

testthat::test_that("say_hello works", {
  testthat::expect_equal(say_hello("Jacob"), "Hello Jacob!")
  testthat::expect_equal(say_hello("Jacob", exclamation = FALSE), "Hello Jacob.")
})

## Test passed

Code chunks that have one or more lines starting with test_that( (or testthat::test_that() are added to the package as tests.

Documenting the package and building

We finish by running commands that will document, build, and install the package. It may also be a good idea to check the package from within this file.

litr::document() # <-- use instead of devtools::document()
# devtools::build()
# devtools::install()
# devtools::check(document = FALSE)

## ℹ Updating rhello documentation
## ℹ Loading rhello
## Writing 'NAMESPACE'
## Writing 'say_hello.Rd'