Dependencies

When and how to import

Resources:

• Chapter 10, 11 from the R package book (2e) by Hadley Wickham

Ongoing notes

Some of the content are being added as I go.

Packages in Imports and Depends

Inside DESCRIPTION, there are three categories of dependencies: imports, suggests and depends. For now focus on imports and depends.

Generally, three ways to call a function in a dependency:

• use deppkg::function();
• use Roxygen2 tag @importFrom deppkg function, then call this particular function directly;
• use Roxygen2 tag @import deppkg and call anything directly.

Imports

Packages are required to make functions run, but are NOT loaded when loading your own package.

When a pkg is listed in DESCRIPTION under Imports: recommended to call with deppkg::function() syntax.

my_function <- function(x,y){
  z <- dplyr::select(...)
}

Avoid importing anything with @import tag, so that it is easier to understand what function is not local.

Depends

Very similar to Imports, but loaded when your package is loaded.

However, even after putting pkg (such as ggplot2) under Depends, you still need to call the functions in a correct way (the three options above).

Common error, warning and notes

Error: could not find function xyz

Where the function xyz is from a dependency package, such as ggplot2.

could not find function “ggplot”

This happens when dependency package such as ggplot2 is not imported. When checking NAMESPACE, you see that this package is not in the import list.

To tackle this, locate the function where the error occurs, add the Roxygen2 tags as appropriate:

#' @importFrom aaapkg aaa_fun
#' @import bbbpkg
#' @export
my_function <- function(x,y){
  ...
}

Then document (either devtools::document() or Build -> Document button). Check NAMESPACE again, see if the package is imported.

Note: all declared imports should be used

Namespaces in Imports field not imported from: ‘data.table’ ‘gt’ ‘gtExtras’ ‘magrittr’ ‘rlang’ All declared Imports should be used.

This might happen when these external packages are not used. I can be more explicit when I actually use these packages somewhere. See 11.4.1 of the book for more information.