I am currently developing an R package that make use of different datasets from other R packages. As a result, my package has a large number of dependencies, and the user is required to install various unrelated packages in order for my package to work.
I would prefer to copy these datasets to my own package and give proper credit in the documentation, but is there a problem with that?
And what about simple functions from other packages? For example, I need the Matern function from the fields package, and it seems much simpler to just copy that function to my own package instead of having a dependency on a whole package full of unrelated functionality.
Why not just ask the authors/maintainers of those packages for their permission or thoughts on the matter? They may know something that the rest of us don't about how the functions are implemented and how easy they are to copy.
Two different people asked me if they could include a function from my package in theirs, they explained why they wanted to and what they were doing and I agreed that having the user install my whole package for just the 1 function would be overkill and gave them my blessing (and the original source code) to include the functions in their packages (technically due to the license they did not need my permission). Now when I update either of the functions, I also send the updated source code to those 2 authors so that they can keep their copy up to date if they want to.