Using external data from within another package

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If you make the error which I did, you will try to use the data (say, “pckgdata”) from another package (say, “pckg”) naively like this:

someFunc <- function() {
  data(pckgdata)
  foo <- pckgdata$whatever
}

This will result in an error:

someFunc: no visible binding for global variable ‘pckgdata’
someFunc : <anonymous>: no visible binding for global variable
  ‘pckgdata’
Undefined global functions or variables:
  pckgdata

Here is the solution (thanks to the comments from stackexchange:

.myenv <- new.env(parent=emptyenv())

someFunc <- function() {
  data("pckgdata", package="pckg", envir=".myenv")
  foo <- .myenv$pckgdata$whatever
}

Actually, let us load the object as soon as our package is loaded:

.myenv <- new.env(parent=emptyenv())

.onLoad <- function(libname, pkgname){
  data("pckgdata", package="pckg", envir=".myenv") 
}

someFunc <- function() {

  foo <- .myenv$pckgdata$whatever
}

Now any of the functions in our package can use the pckgdata, whenever. Note that we want to use .onLoad(), and not .onAttach() — the latter one is for such things as startup messages when the package is manually attached by the user.

Alternatively, you can create your environment within the function itself:

<br />someFunc <- function() {
  myenv <- new.env(parent=emptyenv())
  data("pckgdata", package="pckg", envir="myenv")
  foo <- .myenv$pckgdata$whatever
}

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This article is originally published at https://logfc.wordpress.com
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