How can I load dependencies in an R package?

Question

I am developing an R package where this is available in the DESCRIPTIONS file

Imports: 
    dplyr,
    ggplot2,
    ncdf4

And I have an example function where I use the third dependency

testFun <- function(file, lat, long){
  ncfname <- file.path(file,fsep = .Platform$file.sep)
  xfile <- nc_open(ncfname) #Opens the NetCDF file
  lat <- ncvar_get(xfile, 'lat') #Extracts all latitudes

  ...Calculations

  return(XYZ)
}

When I Build and Reload the package, and I run the function, it could not find function "nc_open".

BUT, it works when I replace it with ncdf4::nc_open

Am I supposed to prefix packagename:: to every dependency I use in the code? or am I missing something?

Ordinarily, I would like all the dependencies to be installed from the DESCRIPTIONS and it's functions available for use without requiring the package prefix everytime.

Answer 1

The easiest way and most correct way is to directly pull your function from the package without opening any packages which might obliterate someone's current environment.

Try this:

xfile <- ncdf4::nc_open(ncfname)

It should access what you need without conflicts. That is the current preferred method because it leaves things as it found them for your users. It also makes it easy for people to KNOW what is happening should they go exploring.

Answer 2

Either:

• explicitly prefix the function with the package it's from: ncdf4::nc_open(...)

Or:

• add a line in your NAMESPACE file importFrom(ncdf4, nc_open) and then in your code, call the function without the package: nc_open(...)

Rather than adding an importFrom line for every function you want to import, you can also use import(ncdf4) to snarf everything from that package.