R: use magrittr pipe operator in self written package

问题

I would like to use the pipe-operator %>% introduced in the magrittr package in a package I wrote myself to chain dplyr data transformations. magrittr is listed as Import in the DESCRIPTION file. After loading my own package and testing the function which uses the pipe-operator I get the following error message:

Error in functionname(parameter, : could not find function "%>%"

Changing %>% to magrittr::%>% in the function source code does not help either because the package cannot be built anymore.

回答1:

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.

回答2:

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.

回答3:

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

回答4:

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.

来源：https://stackoverflow.com/questions/54275199/r-package-devtoolscheck-could-not-find-function

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