Wrapping code for sharing and reuse can be done using the following steps:

1. Load an existing source code file:

source(file.path(getwd(), "datasets", "ch11", "my_source_file.R"))
my_sourced_function()

2. Create a package skeleton:

usethis::create_package("newpackage")

3. Write code:

my_package_function <- function(x){
 return( c("I come from a package!") )
}

4. Load the package code into memory:

devtools::load_all()

5. Install the package into your current R installation:

devtools::install()
library(newpackage)