Use RStudio and the devtools package. It's easier.

install.packages("devtools")

In RStudio, File -> New Project -> New Directory -> R Package, with a name:

• must start with letter
• no underscores
• periods allowable or use CamelCase
• can have numbers

Go to Build -> Configure Build Tools

Add --as-cran to "Check Package" (useful later)

Click Generate documents with Roxygen. If that is gray, install roxygen2:

install.packages("roxygen2")

Click "Configure" - click all the boxes.

• Delete the man folder
• roxygen2 will create the documentation automatically
• Delete NAMESPACE file (we will discuss later)
• roxygen2 will create the documentation automatically

In the RStudio project, go to "Go to file/function" search bar on the menu bar.

• This searches through the files in the package.
• Also searches for function names and can go to that function in the file

Type "DESCRIPTION" and open that file.

• "Title - What the Package Does (Title Case)
• "Author: YOURNAME"
• "Maintainer: YOURNAME your@email.com"
• "Description: Use paragraph prose here. Don't start with word package" Use four spaces when indenting paragraphs within the Description.
• "License: ", one of GPL-2 GPL-3 LGPL-2 LGPL-2.1 LGPL-3 AGPL-3 Artistic-2.0 BSD_2_clause BSD_3_clause MIT

• Imports: package1, package2
• packages with specific functions called in package
• Depends: package3, package5
• packages with ALL functions loaded from package
• Suggests: package4, package6
• used in examples or vignettes

Roxygen allows for functions and documentation in the same file. Let's make a function:

top = function(x, n) {
  xx = x[1:n, 1:n]
  hist(xx)
  print(xx)
}

Save this to top.R file in R/ (where R functions are). Delete hello.R file.

Highlight the following code:

top = function(x, n) {

Go to Code -> Insert Roxygen Skeleton

Output:

#' Title
#'
#' @param x 
#' @param n 
#'
#' @return
#' @export
#'
#' @examples

Add @title and @description tags:

#' @title
#' @description
#'
#' @param x 
#' @param n 
#'
#' @return
#' @export
#'
#' @examples

• @param stands for a parameter/argument for that function.
  
• @return denotes what the function returns. This is required.
  
• @export - when people install your package, can they use this function
• non-exported functions are usually helpers, really small, or not fully formed yet
• @examples - code to show how the function works. Wrap functions in \dontrun{} if not wanted to run

#' @title Print the top of a matrix
#' @description \code{top} is a small function to not just present the first rows
#' of a matrix, but also the first number of columns
#'
#' @param x a \code{matrix}
#' @param n Number of rows and columns to display of the matrix
#'
#' @return A \code{NULL}
#' @export
#'
#' @examples 
#' mat = matrix(rnorm(100), nrow = 10)
#' top(mat, n = 4)
#' \dontrun{
#'    top(mat, n = 10)
#' }

The NAMESPACE files tells the R package what to import and export. In Roxygen:

• @export - adds this to the NAMESPACE file
• when package is installed, users can call this function
• @import - in roxygen, if you want to import a package, you say @import PACKAGENAME
• imports ALL functions from that package
• if package is listed under Depends in DESCRIPTION, then the whole package is loaded when you load your package
• otherwise it simply exposes them for your package to use them, but not the user, users still have to do library(PACKAGENAME)

• @importFrom - in roxygen, if you want to import a function, you say @import PACKAGENAME func1 func2
• only imports these functions. Better way of doing things.
• if pkgA has function A and pkgB has functions A and B, if @import pkgA A, @import pkgB B, then if you call A(), R knows it's from pkgA
• you must import anything explicitly other than from the base package, includying anything from stats (e.g. quantile) or graphics (e.g. hist)

Add @importFrom graphics hist to your top.R file

• Go to Build -> Build and Reload the package
  • First time you may see some warnings (no NAMESPACE file!)
  • Rerunning should get rid of these
  • look in the folders
• Then try Build -> Check Package