[Rd] Citation if copying R base code

[Peter Meissner]

Dear Listeners,

... also I read the CRAN policies and tried to solve those questions 
myself I feel very much in the need of good advise ...


I am currently finishing a package that -- to solve some nasty problems 
with dirty data -- uses its own as.Date() equivalent methods (i.e. its 
own generic and methods).

Thereby, I shamelessly copied code from the as.Date() methods from the 
base package and only made some minor adjustments.

For my main achievement was copy-pasting I feel obliged to cite the 
efforts made by base package authors - do I, should I? Currently I only 
use the help files to mention that the generic and its methods are 
basically the same as as.Date(), except this and that.

And if yes how to do it best? What is the standard procedure here? 
Should I include base package authors as contributors in DESCRIPTION???

Am I allowed to use MIT + file license with that or is it wrong to do so?


I appreciate any advise on these (I think important) but very confusing 
matters of referencing and licensing.


Best, Peter


PS:
- My current description:
https://github.com/petermeissner/wikipediatrend/blob/master/DESCRIPTION

- the package specific as.Date() implementation:
https://github.com/petermeissner/wikipediatrend/blob/master/R/wp_date.R