How to add a list to exported data when building up R packages?

I save two lists as ".RData" in the my_package/data and have their documentation in /R. But after installation, I cannot load those two lists but it shows the help documentation. Is it possible to export a list in a R package? Or just able to matrix or something like that. I am confused by "one object in one .Rdata file"

Solution

Hadley's online book R Packages (and particularly the chapter on data) does a more thorough job of describing how to include data, but I'll walk through how to make arbitrary objects useful in a package.

Up front:

one has private data (accessible to same-package functions without change, accessible outside of the package using :::) and public data (data available to both internal functions and whomever loads the package, optionally lazy-loaded)
public data is stored in the ./mypackage/data/ directory, and it shall use the *.rda extension (*.Rdata) does not work; a common convention (for version-control, convenience, maintainability) though not a strict requirement is for one object per .rda file, and named as the object name; below, I stored mypubliclist in ./mypackage/data/mypubliclist.rda;
private data should all be saved in one file, ./mypackage/R/sysdata.rda.

Here's a sample package (I'm using devtools, but there are other ways to do so):

devtools::create("~/StackOverflow/14489611/mypackage")
# v Creating 'C:/Users/r2/StackOverflow/14489611/mypackage/'
# v Setting active project to 'C:/Users/r2/StackOverflow/14489611/mypackage'
# v Creating 'R/'
# v Writing 'DESCRIPTION'
# Package: mypackage
# Title: What the Package Does (One Line, Title Case)
# Version: 0.0.0.9000
# Authors@R (parsed):
#     * First Last <first.last@example.com> [aut, cre] (YOUR-ORCID-ID)
# Description: What the package does (one paragraph).
# License: `use_mit_license()`, `use_gpl3_license()` or friends to pick a
#     license
# Encoding: UTF-8
# LazyData: true
# Roxygen: list(markdown = TRUE)
# RoxygenNote: 7.1.1
# v Writing 'NAMESPACE'
# v Changing working directory to 'C:/Users/r2/StackOverflow/14489611/mypackage/'

I wrote a small script ./data-raw/mylist.R to create some random data. This file is merely for reproducibility, it is not referenced during package production or loading.

set.seed(42) # R-4.0.2
myprivatelist <- list(a = sample.int(10), b = sample.int(1e5))
mypubliclist <- list(a=1:10, b=11:20)
save(mypubliclist, file="~/StackOverflow/14489611/mypackage/data/mypubliclist.rda")
save(myprivatelist, file="~/StackOverflow/14489611/mypackage/R/sysdata.rda")

I also created an R file ./mypackage/R/data.R (you can name this file anything, but it must be under ./mypackage/R) to contain simple documentation for these lists:

#' My private list
#' @format list with random numbers
"myprivatelist"

#' My public list
#' @format list with not-so-random numbers
"mypubliclist"

And now generate documentation:

devtools::document("C:/Users/r2/StackOverflow/14489611/mypackage")
# Updating mypackage documentation
# Loading mypackage
# Writing myprivatelist.Rd
# Writing mypubliclist.Rd

I'll build the package, restart R, install and then load the datasets.

devtools::build("~/StackOverflow/14489611/mypackage")
# v  checking for file 'C:\Users\r2\StackOverflow\14489611\mypackage/DESCRIPTION'
# -  preparing 'mypackage':
# v  checking DESCRIPTION meta-information
# -  checking for LF line-endings in source and make files and shell scripts
# -  checking for empty or unneeded directories
#      NB: this package now depends on R (>= 3.5.0)
#      WARNING: Added dependency on R >= 3.5.0 because serialized objects in  serialize/load version 3 cannot be read in older versions of R.  File(s) containing such objects: 'mypackage/R/sysdata.rda'  'mypackage/data/mypubliclist.rda'
# -  building 'mypackage_0.0.0.9000.tar.gz'
#    
# [1] "C:/Users/r2/StackOverflow/14489611/mypackage_0.0.0.9000.tar.gz"

## restart R
install.packages("C:/Users/r2/StackOverflow/14489611/mypackage_0.0.0.9000.tar.gz")
# Installing package into 'C:/Users/r2/R/win-library/4.0'
# (as 'lib' is unspecified)
# inferring 'repos = NULL' from 'pkgs'
# * installing *source* package 'mypackage' ...
# ** using staged installation
# ** R
# ** data
# *** moving datasets to lazyload DB
# ** byte-compile and prepare package for lazy loading
# ** help
# *** installing help indices
#   converting help for package 'mypackage'
#     finding HTML links ... done
#     myprivatelist                           html  
#     mypubliclist                            html  
# ** building package indices
# ** testing if installed package can be loaded from temporary location
# *** arch - i386
# *** arch - x64
# ** testing if installed package can be loaded from final location
# *** arch - i386
# *** arch - x64
# ** testing if installed package keeps a record of temporary installation path
# * DONE (mypackage)

And let's see what worked:

str(mypubliclist)
# Error in str(mypubliclist) : object 'mypubliclist' not found
#     x
#  1. \-utils::str(mypubliclist)
library(mypackage)
str(mypubliclist)
# List of 2
#  $ a: int [1:10] 1 2 3 4 5 6 7 8 9 10
#  $ b: int [1:10] 11 12 13 14 15 16 17 18 19 20
str(myprivatelist)
# Error in str(myprivatelist) : object 'myprivatelist' not found
#     x
#  1. \-utils::str(myprivatelist)
str(mypackage:::myprivatelist)
# List of 2
#  $ a: int [1:10] 1 5 10 8 2 4 6 9 7 3
#  $ b: int [1:100000] 47128 16740 61605 73236 9091 62041 33700 59359 54789 54586 ...

And its documentation, if you're curious. (I use print because otherwise it'll pop up in the other pane; this just dumps it to the console.)

print(help("mypubliclist"))
# mypubliclist             package:mypackage             R Documentation
# My public list
# Description:
#      My public list
# Usage:
#      mypubliclist
#      
# Format:
#      list with not-so-random numbers
print(help("myprivatelist"))
# myprivatelist            package:mypackage             R Documentation
# My private list
# Description:
#      My private list
# Usage:
#      myprivatelist
#      
# Format:
#      list with random numbers