[R] Importing only one function from a package

[Deepayan Sarkar]

On 9/28/07, Søren Højsgaard <Soren.Hojsgaard at agrsci.dk> wrote:
> Dear List
>
> In a package I want to import the mApply function from the Hmisc package, and I would like to import only that function.
>
> 1) If I write "Depends: Hmisc" in the DESCRIPTION file I get the whole Hmisc package, so that is not the way to go ahead.
>
> 2) According to "Writing R extensions", sec 1.6.1 "Specifying imports and exports" I can (as I read it) simply type Hmisc:::mApply(....) in my code. That works, but gives a warning in the check:
>
> * checking for unstated dependencies in R code ... WARNING
> '::' or ':::' imports not declared from:
>   Hmisc
>
> 3) According to the same section I can (again as I read it) write in the NAMESPACE file
> importFrom(Hmisc,mApply)
>
> Then I get:
>
> * checking package dependencies ... ERROR
> Namespace dependencies not required:
>   Hmisc
>
> That message goes away if I write  "Depends: Hmisc" in DESCRIPTION, but then
> we are back to 1) where I started where the whole Hmisc package is loaded.
>
> Obviously I have missed a point or two somewhere. Can anyone enlighten me?

For both 2) and 3), the correct DESCRIPTION entry is

Imports: Hmisc

And for 2), you should be able to use Hmisc::mApply (i.e., 2 colons,
not 3), although 3) is preferred.

-Deepayan