How to automatically load functions into namespace of an R package

I have an R package that requires functions from several other packages to be in the namespace. Using roxygen2 documentation, I've successfully installed these packages (i.e. install.packages(dplyr)), but I am unable to load them in automatically (i.e. library(dplyr)).

Here is my DESCRIPTION file:

Package: pkgname
Title: What the Package Does (one line, title case)
Version: 0.0.0.9000
Authors@R: person("First", "Last", email = "[email protected]", role = c("aut", "cre"))
Description: What the package does (one paragraph).
Depends: R (>= 3.5.2)
Imports:
  ggplot2,
  zoo,
  tidyr,
  dplyr,
  magrittr
Suggests:
  RColorBrewer
License: What license is it under?
Encoding: UTF-8
LazyData: true
RoxygenNote: 6.1.1

At the end of the documentation for one of my functions that requires the pipe function from magrittr, I included the following notation:

#' @importFrom magrittr %>%
#'
#' @export
funName <- function(...) { 
... 
}

And the other function:

#' @import ggplot2
#' @importFrom magrittr %>%
#'
#' @export
funName2 <- function(...) {
...
}

And this successfully shows up in my NAMESPACE file:

# Generated by roxygen2: do not edit by hand

export(funName2)
export(funName)
import(ggplot2)
importFrom(magrittr,"%>%")

However, despite the added notation in roxygen2 comments and the correct script in my NAMESPACE file, I still have to load the packages ggplot2 and magrittr using library(package-name) at every new R session. I expect this requirement for dplyr, tidyr and zoo (since I do not explicitly load these, just install them), but I did not for ggplot2 or the %>% operator. Am I importing them incorrectly?

Solution

You should never use library(package.name) inside your package functions. Instead use package.name::function.name(). You need to re-export the magrittr pipe operator:

1- put magrittr into the DESCRIPTION file (as you did)

2- make an __imports.R file to the packages R/ directory with the following lines:

#' re-export magrittr pipe operator
#'
#' @importFrom magrittr %>%
#' @name %>%
#' @rdname pipe
#' @export
NULL

Or, similarly do as Hadley Wickham says:

#' Pipe operator
#'
#' @name %>%
#' @rdname pipe
#' @keywords internal
#' @export
#' @importFrom magrittr %>%
#' @usage lhs \%>\% rhs
NULL

I think you can do the same for other imports when necessary. Use @importFrom as much as you can, otherwise re-export it.