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

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.