R: use magrittr pipe operator in self written package

Question

It should have worked correctly if you had magrittr listed in Depends. However, this is not advised. Instead, you leave magrittr in Imports and add the following line to NAMESPACE:

importFrom(magrittr,"%>%")

I suggest reading Writing R extensions. Your question is covered in paragraphs 1.1.3 and 1.5.1.

There's now an easier way to support the pipe in your packages. The wonderful package usethis has the function use_pipe(). You run that function once and it handles everything. This is how the use_pipe() function is described in the usethis documentation:

Does setup necessary to use magrittr's pipe internally in your package and to re-export it for users of your package:

Adds magrittr to "Imports" in DESCRIPTION

Creates R/utils-pipe.R with the necessary roxygen template

One additional solution - use the roxygen package. It's implemented as part of the devtools package. Once devtools is installed, calling devtools::document() will update your NAMESPACE for you. It also auto-builds .Rd files with documentation, which is handy.

All you do is add a special comment in the format #' @import packagename to a file to import all functions from that package, or #' @importFrom packagename functionname to import a function. You can have as many of these comments as you want in your files, so you can have a set of them at the top of each file, or with each of your functions that needs an external function.

Then you run devtools::document() and it parses your code looking for those comments, and then it creates an appropriate NAMESPACE file for you. Easy.

Assuming that you're using RStudio, Hadley's devtools package, and listed magrittr in the Imports section of the DESCRIPTION file, here are steps I took to make %>% work in my package function(s).

First, write function foo.R:

#' Convert \code{data.frame} to \code{list}.
#' 
#' @importFrom magrittr %>%
#' @name %>%
#' @rdname pipe
#' @export
#' @param x A \code{data.frame} object.
#' @examples
#' my_result <- foo(iris)
#'
foo <- function(x) {
    x %>%
        as.list()
}

Second, run devtools::document().

Third, run devtools::load_all().

A file like this will be created in your R/ directory and your function should work as expected.